Updated

United Nations Ambassador Samantha Power says the United States is concerned that the most dangerous terrorist groups could get a hold of chemical weapons if Syria is hiding any stockpiles.

Power spoke to reporters after the Security Council received a briefing from Sigrid Kaag, who heads the international effort to rid Syria of its chemical weapons.

The joint mission of the United Nations and the Organization for the prohibition of Chemical Weapons will end at the end of the month after destroying nearly all of Syria's declared stockpile. But Kaag said the OPCW is still working with Syria to resolve discrepancies in its declaration.

If President Bashar Assad is hiding any stockpiles, Power said they could fall into the hands of "extremist groups who have committed some of the most vile acts in the last few days."