welcome to bbc news, broadcasting to viewers in north america and around the globe. i'm reged ahmad. our top stories: a wave of toxic destruction — dramatic new footage shows the moment a dam collapsed in brazil. at least 110 people are dead and more than 200 still missing. the question that everyone here isjust stunned by is how, in a big, modern, growing economy, this could ever have been allowed to happen. russia condemns america's decision to pull out of a nuclear disarmament treaty signed during the cold war. the us says moscow's new cruise missile violates the terms of the deal. we have a special report from venezuela, where opponents of nicholas maduro say they've been detained and tortured in the past few days. facebook loses two of its key fact—checking partners, prompting questions about how committed it is to rooting out fake news. dramatic pictures have emerged

of the moment a dam burst in brazil, releasing millions of tonnes of mining waste that engulfed nearby buildings. at least 110 people are now known to have died in the disaster, which happened in the state of minas gerias last month. at least 200 are still missing. our science editor, david shukman reports from the site of the dam, in the south east of brazil. first, a long cloud of dust, then a nightmare vision of an unrelenting torrent of sludge, the waste from decades of mining racing towards hundreds of unsuspecting people down below. the catastrophe unfolded a week ago, but only now has this video come to light, adding to the sense of loss and of outrage. and difficult for you.

this red cross volunteer, henato silveira, leads me to the edge of the disaster zone. seis corpos. six bodies. he alone has found six bodies. any hope of reaching survivors in this endless sea of mud was quickly dashed. emergency workers are now scouting for any signs of bodies from the air, and they are picking their way over this horrific landscape. we spotted this search team with a sniffer dog in the distance. by the time the wall of mud reached this point, it had already overwhelmed the cafeteria where the miners were having lunch and destroyed the offices of the mine itself, before arriving here, tearing through a hotel and holiday chalets, before surging on over that ridge in the distance and down into the valley beyond, where it caused yet more destruction. and the question that everyone here isjust stunned by is how, in a big, modern, growing economy,

this could ever have been allowed to happen. investigators are now on the scene. the dam holding back the waste was owned by one of the world's largest mining companies. it was inspected only last year. we find a local man, leandro gil, praying for friends lost in the mud. "unfortu nately", he says, "someone just thought about himself. he didn't protect the dam properly. so, after years and years, that's now been revealed." a special mass, seven days since the disaster. there is grief and anger, and the demand for answers will only grow. david shukman, bbc news, in brazil. could the world be on the verge of a new nuclear arms race between the us and russia? that's the question being asked, after the us suspended a landmark deal which has been in force for more than three decades. it's accusing russia of breaking it — something russia denies. the agreement in question outlaws the use of

intermediate range nuclear missiles stationed on land. laura westbrook reports. in 1987, us president ronald reagan and soviet leader mikhail gorbachev signed the intermediate—range nuclear forces treaty. it led to hundreds of missiles in both countries being destroyed. three decades later, the us secretary of state three decades later, the us secretary of state made this announcement. russia has jeopardised the united states‘ security interests, and we can no longer be restricted by the treaty while russia shamelessly violates it. nato agrees with the decision by the united states. we continue to call on russia to come back into compliance in a verifiable way, because we don't want a new arms race. this wasn't unexpected. for years, america has been consigned about russia's testing and deployment of a cruise missile that it says breaches the inf treaty.

there's concerns other countries, including china, aren't tied by the accord. for now, the treaty is suspended. the us could pull out formally in six months, but gave russia a final chance to save the deal. i hope that we're able to get everybody in a very big and beautiful room, and do a new treaty that would be much better, but — because certainly i'd like to see that. for its part, the kremlin says this was a political decision. russia denies the missile in question is in violation of the treaty. this was iran's response. the foreign minister tweeted. .. this was the image that let the world know the cold war was coming to an end. 30 years later, many are concerned about the future of nuclear arms control. laura westbrook, bbc news.

professor matthew bunn is a nuclear expert at harvard university. he was also a white house science and technology adviser. thank you for your time. what could be the consequences of the us permanently pulling out of this treaty? i think we are going to see some serious disputes within the nato alliance. the last thing the european countries want is another huge set of protests over deployment of nuclear missiles in the way we had in the 1980s. but really the united states is not that interested in the plight nuclear missiles in europe. the issue is more asia where china is not limited by this treaty and has missiles there some in the

united states would like to counter. i think it was a mistake to announce its suspension of ultimate pullout from this treaty and that there would still be opportunities to negotiate a broader package with russia that would include dismantling the missiles in question in russia. if you say this treaty, as if you say, china is a real threat, is the treaty a little bit outdated, perhaps the treaty needs to go? i do not think so. i think the united states can easily counter china ‘s capabilities with sea and air base systems that are not limited by the treaty. i think the treaty retained substantial security value but, of course, we do have to respond to the russian cruise

missile which i agree with the us government does have prohibited range. i think rather low than simply going to the russians and demanding you must confess to your violation and then dismantle the system without the western doing anything, i think what should be done is for the united states to put forward a broader package that it believes service us interests but would also serve russian interests and would include russian dismantling these missile as full as united states adding provisions to its ground—based missile defences which russia complains about because they campfire cruise missiles, to make clear the base land one cannot fire missiles of that kind. are we going to see an arms race now? does

russia have the fund and appetite? russia have the fund and appetite? russia is building a whole new generation of strategic weapons. the us is organising its nuclear weapons. i do not think we will see a race in numbers but new and different type of strategic weapons. it isa different type of strategic weapons. it is a very dangerous situation will not i think we need to take action now to take down the attention and to rebuild the whole structure of nuclear arms control that has given us the predictability in monitoring that has helped. thank you very much for your time. let's get some of the day's other news: the court of arbitration for sport has banned 12 russian athletes for doping. they include the london olympics highjump gold medallist ivan uskov and svetlana shkolina, who won gold at the 2013 world championships. both were given four year bans. the americans who won silver will inherit the gold. the offences of all 12 athletes date back to those sporting events.

the italian authorities have impounded the last charity rescue ship operating in the central mediterranean. the sea watch iii was detained after being allowed to disembark 47 migrants in the sicilian port of catania. italy's populist government has been trying to stop humanitarian groups from bringing rescued migrants ashore. authorities in the united states fear the death toll linked to the deep freeze may rise. at least 21 people have died during the cold snap. the mercury plummeted to —30 degrees celsius in places, like chicago, but the icy conditions have started to ease. emergency services are bracing for the ice and snow to melt, increasing the chance of urban flooding and mudslides. venezuela's opposition leader juan guaido is calling for the biggest mass protests in the nation's history this weekend as he tries to force president nicholas maduro from power. the opposition are demanding new elections, to end the political and economic chaos engulfing the country.

human rights lawyers have told the bbc there's been a wave of political arrests, with almost 1,000 people detained in recent days. the government denies it tortures prisoners. but our international correspondent 0rla guerin has heard a harrowing account from one women, who says she was beaten and abused. you may find some of 0rla's report upsetting. under darkened skies, caracas waits. some here hoping for a modern—day liberator to replace president nicolas maduro. but those who dare to oppose him can expect to pay a price. almost 1,000 people have been detained in the past 10 days. we're on our way now to meet one of them. she's a young woman who we can't identify for her own safety. she's just been released and she has a harrowing story to tell. she says she was held

in this building, the headquarters of the military police. they interrogated her about a relative, a military officer suspected of plotting against the president. translation: they tortured me. they put a plastic bag over my face and choked me. then they put my head in a bucket of water to try to drown me. i fainted and they beat me, to wake me up. they put a gun in my mouth and cocked it. they said they wanted answers fast, and that they loved to see people suffer. their boss told them all to rape me. they lifted my shirt and took off my bra and they touched me. did you think that you might be killed? translation: yes, because they were constantly saying it. they said they were going to kill me

and throw me in the river. they said, "we are the government "and nobody can do anything against the government". and eading human rights lawyer alfredo romero says venezuela's government is in overdrive, trying to silence dissent. now we can talk also about generalised persecution, generalised detentions. that they detained anyone in order to intimidate people and produce what they are producing, this fear of protesting. and that's what is going on. but some, like federica romer, a politics student, are determined to keep up the fight. she says being a mother to 6—month—old carlota means she has to protest. this is for her, you know? this is for her. before i had her, ifelt

invincible and i did not care. and now that i have her, of course, i'm scared to go out. i'm terrified. but this is absolutely for her, you know? ‘cause she is the next generation of this country. they are the ones who are going to hold this country up. federica is preparing to go back out on the streets tomorrow at a mass demonstration called by the opposition, gas mask at the ready. 0rla guerin, bbc news, caracas. much more background on the venezuelan situation now website. stay with us on bbc news, still to come: another democrat jumps into the presidential race. senator cory booker is trying to convince voters that he's the right candidate to take on president trump. this is the moment that millions

in iran had been waiting for. after his long years in exile, the first hesitant steps of ayatollah khomeini on iranian soil. south africa's white government has offered its black opponents concessions unparalleled in the history of apartheid. and the anc leader, nelson mandela, is to be set free unconditionally. ..four, three, two, one... a countdown to a critical moment. the world's most powerful rocket ignited all 27 of its engines at once. and, apart from its power, it's this recycling of the rocket, slashing the cost of a launch, that makes this a breakthrough in the business of space travel. two americans have become the first humans to walk in space without any lifeline to their spaceship. one of them called it a piece of cake. thousands of people have given the yachtswoman ellen macarthur a spectacular homecoming in the cornish port of falmouth, after she smashed the world record for sailing solo around the world non—stop. this is bbc news,

the latest headlines: dramatic new footage has emerged, showing the moment a dam collapsed in brazil. at least 110 people are confirmed dead the united states suspends a major cold war arms agreement with russia, saying it's violated the treaty with a new missile system. the democratic field to take on president trump in the 2020 elections is getting more crowded by the day. the latest entry is senator cory booker from newjersey. he's the fourth senator on the current list of candidates, and the second african—american. booker is hoping a message of optimism and unity will set him apart. jane 0'brien reports. voiceover: in america, we have a common pain. but what we are lacking is a sense of common purpose. cory booker, the charismatic

senatorfrom newjersey, has been positioning himself for a presidential bid for some time. and like many of his rivals, his official declaration has come early. he portrays himself as somebody who can bridge america's political, racial and economic divides, making his formal pitch outside his home in a low—income neighbourhood. i believe in the american people, i think they will look to the democratic party for leadership, i believe we are going to consolidate this country against the politics of hate, politics of division. in a crowded field that now includes four senators, name recognition is key. the candidate must also make clear their differences. i imagine that the crowded democratic field of presidential aspirants will be attacking each other‘s records or lack thereof, so we will be sitting back with copious bowls of popcorn watching that. but booker, who has made civil rights and racial injustice the cornerstone of his political career, shows no sign of mudslinging. at least not yet. how is my hair?

is there anything hanging out of my nose? that is a real friend who tells you to truth. that is cory booker with senator kirsten gillibrand, one of the record number of women throwing their hat into the ring. the first to congratulate him. i am cory booker, one of kirsten gillibrand's best friends in washington. and bernie sanders. the former vice president has yet to declare that he is the 800—pound gorilla in the room. he is known, he is liked, and he is moderate. and in a showdown with donald trump that might give him the edge. two of the companies brought in by facebook to sift out fake news say they're pulling out of the deal. snopes, one of more than 30 fact—checking operations working with facebook, pulled out earlier on friday, and the associated press has also now confirmed to the bbc that it too has ended its deal.

our technology correspondent, dave lee, has this report from san francisco. 0r or was one of the most well—known organisations working with facebook as it attempted to get on top of it is rather last misinformation problem. the fact the company has now pulled out from the deal is pretty embarrassing. in a statement snopes said there were many is to be amending the partnership it seemed that money was at the heart of it. it said the company did not think it was worthwhile continuing to do their work. but it has been suggested the company would not rule out working with facebook in the future if it was to change the terms of how they did their fact checking on the platform. facebook said value the contribution of snopes and insisted that it has more than 30 different fact sheet has around the world and that it still took the problem very seriously. new research out of stanford and new york university takes a look at what happens when people step back from facebook for a month.

the study, entitled the welfare effects of social media, finds that disengaging from the social networking site leads to lower online activity, reduced knowledge of current events and ‘small but significant improvements in wellbeing'. david ryan polgar is a tech ethicist and founder of all tech is human. hejoins me now. in some ways, we have often heard, quite recently actually, about the benefits of switching from facebook, is there anything in this study that surprised you? 0ther other parts surprised me. i was surprised that there was not a social media... if they eat did not go to other websites. they actually switched off, they spent more time with family and friends, and had

those reported increases in happiness. what i found interesting was the reduced factual news knowledge but also reduced political polarisation. what do you think that that element of the study tells us? it shows that there is a potential positive to facebook, which are not view it in binary terms, as either good or bad, it obviously has positive parts of society, and i think a lot of people get their news from facebook. but to your point, it increases polarisation. what the study did not really get into in—depth, which a lot of commentators have talked about recently, is this idea of echo chambers, one of the issues is that we might be getting our news from facebook, but because of their algorithmic bias towards higher engagement, they might be showing us news that goes to our preconceived notions about political parties or leanings, which in terms might increase polarisation, which is part

of the problem we are having. there are, as you say, some positives with facebook. a lot of people who use it to organise their social lives, and switching off at would mean that they miss out on a lot of events. it's they miss out on a lot of events. it‘s not that easy to come off the site. no, and i think the issue is that we should not unplug, we should plug indifferently. the biggest part i took away from this study is that it was kind of these participants, they got off the hamster wheel and said, i don‘t necessarily not want tojump, said, i don‘t necessarily not want to jump, hamster wheel of social media, ijust to jump, hamster wheel of social media, i just want to engage differently. i don‘t want be disengaged, ijust differently. i don‘t want be disengaged, i just want to engage differently. i don‘t want be disengaged, ijust want to engage in a matter that is betterfor disengaged, ijust want to engage in a matter that is better for my own life. additionally, what i think facebook does well with is, it increase —— increases the breadth of oui’ increase —— increases the breadth of our connections. what we as humans find a lot of value in is the depth of our conversations, the depth of oui’ of our conversations, the depth of our relationships. that is the bigger takeaway from the study, we need to focus on notjust the break

but also the depth, we need to have close friends that we can have interesting conversations with, we need to engage with our family and other loved ones we have, that is the key part, facebook or any social media is not going to be a replacement, it‘s going to be a conduit, which should hopefully lead to those off—line engagements. conduit, which should hopefully lead to those off-line engagements. we will have to wait and see how many people do switch off, thank you very much for your time. it‘s only a matter of days now until the lunar new year. people in china, korea, vietnam and many other nations in asia will be celebrating. in fact for some, the festivities are already under way, as are the journeys many are taking to be with their loved ones. the bbc‘s tim allman has more. it looks like all of china is on the move. whether it is by train... 0r

plain... 0reven by move. whether it is by train... 0r plain... or even by ship. more than 500 million trips have already been made, nearly 3 billion are expected to be completed before the celebrations come to a close. this man is heading home to set one province, a journey that is expected to last around 30 hours. —— search one. “— to last around 30 hours. —— search one. —— sichuan. this woman is taking her 14—year—old daughter back to their province, which is a snip at only 20 hours. the lunar new year, or spring festival, is associated with light and colour. and if that is what you‘re after, head to this city, where more than 1000 lenders eliminate the night sky. —— lanterns. eliminate. lights ofa sky. —— lanterns. eliminate. lights of a different kind in the north of

china, molten iron thrown into the air. all the while, dragon dancing ta kes pla ce air. all the while, dragon dancing takes place as the redhot metal showers to the ground. translation: it is really amazing when the molten eye and is all through the sky. translation: it is breathtaking seeing people performing the dragon dance against the backdrop of the molten iron sparkles. even these panda cubs were getting into the swing of it at this nature reserve. this will be the year of the pig, so they got to play with some soft cuddly toy versions. no contest as to who was cute though. year of the pig, i hope that rings you lots of luck. stay with us here on bbc world news. we will bring you a lot more on our website as well. hello.

friday was another day with severe transport disruption due to heavy snow. it was across central and southern england that had the worst of it, the billy stretch is of the m3 towards the basingstoke area. particularly stretches is of the m3 towards the basingstoke area. we also had troubles around the m2 in kent as well late in the day. some of those problems were pictured from this area overlooking the m3, you can see how horrendous that conditions look there on the main carriageway, completely covered in snow. transport disruption has been a factor with the forecast through friday, and again into saturday too, with the risk of some snow still around, but ice as well fairly widely. looking at the weather picture over the next few hours, the snow that we have across south—east england is becoming confined to kent before easing away. there will be wintry showers across the eastern side of scotland into eastern parts of england, wherever those showers fall of course that adds to the risk of ice with a widespread and sharp

frost once again. the forecast for saturday is that yes, there will be more wintry weather around, and after a cold and frosty start, icy too, and we will see showers trickling down the eastern coast, probably saying quite cloudy for part of the morning across the maybe with some flurries, but nothing too heavy. chancew of a few showers affecting western wales but they will ease with time. we may see a few showers coming in across the north—west of northern ireland into western scotland. again, showers are a bit of a mixture here with some rain around sea level, we could see some sleet and snow mixed in. saturday, a decent day with some bright or sunny spells after that cold and icy start. temperatures will be struggling once again, looking at another cold day for the time of year. mostly around 3—4 celsius. that goes into saturday night with clear skies leading

to a sharp fall in temperature is the most of the uk. —6 in newcastle, there is the risk of some icy stretches, but further west we will see some cloud thickened as the weather system approaches of the atlantic the sunday. this is going to bring another spell of wintry weather. we could see a few more centimetres of snow, targeting possibly the high ground in northern ireland, but the far north of england and scotland could see maybe 3—6 centimetres, but there is a tendency at lower levels for that snow to transition back to rain as mild air tries to move in from the west. 5—6 for glasgow and belfast. into next week it is all changing, it turns more mild but there will be some heavy rain around as well and it will often be windy. if this is bbc news, the headlines: dramatic pictures have emerged of the moment a dam burst in brazil, releasing millions of tonnes of mining waste that engulfed nearby buildings. more than 100 people are now known to have died in the disaster, which happened in the state of meenas gerias last month. which happened in the state of minas gerias last month. russia has called america‘s decision to suspend

its participation in a key cold war—era disarmament agreement an abrogation of its international commitments. a russian official said washington had provided no evidence of its claim that russia had for years failed to comply with the intermediate—range nuclear forces treaty. venezuela‘s opposition leader, juan guaido, is calling for the biggest mass protests in the nation‘s history this weekend as he tries to force president nicholas maduro from power. the opposition are demanding new elections, to end the political and economic chaos that‘s been engulfing the country. now on bbc news, the week in parliament.