steve o'brien, on a three day visit to syria, said that he is horrified. [ sirens ] >> the blame droppe plane dropped the bomb in a busy marketplace. this town is regularly targeted by syrian government airstrikes, but sunday's attack was the worst yet. civil defense workers and others gathered at the site of the explosion to help move the wounded when more air raids hit. more than 100 people were killed and dozens of others were wounded. doctors at the field hospitals struggled to help those who survived. many of them were critically injured. according to activists on the ground the victims were civilians, women and children were among them. the attacks coincided with the visit of stephen o'brien to syria where he went to the battered city of homs. they have been unable to stop the violence and bring about a political settlement. but they're able to brin bring about the douma strikes. >> attacks on civilians are unlawful, unacceptable, and must stop. i appeal to every party engaged in violence and fighting to protect civilians and to respect international humanitarian law. >> syrian st