. >> shares tumbled as investors worrybo t gbal economy falling back into recession. captioned by the national captioning institute --www.ncicap.org-- >> the united states has demanded that the syrian president step down, and has urged his partners to impose crippling economic sanctions to foe him out. the call was echoed by the european union. washington announced the strongest sanctions to date against the syrian government. >> u.s. president barack obama has said for the first time that the syrian leader should go, and it is too late for him to make the changes needed. secretary of state hillary clinton underlined the message. >> for the sake of the syrian people, the time has come for him to step aside handled leave this transition to the syrians themselves. that is what we will continue to work to achieve. >> the u.s. is introducing further sanctions banning syrian oil products. the tough line was echoed in europe, with leaders in britain, france, and germany calling on the president to leave power. they were not convinced by the claim assad had ended the militar