UNITED NATIONS — The United States is concerned that the Islamic State group and other terrorists could get hold of chemical weapons if Syria is hiding any stockpiles, US Ambassador Samantha Power said Thursday.

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.

Power said the US is concerned not only that President Bashar Assad’s regime still has chemical weapons but that any stockpiles left behind could end up in the hands of the Islamic State group, which has seized large swaths of Syria and Iraq.

“Certainly if there are chemical weapons left in Syria, there will be a risk that those weapons fall into ISIL’s hands. And we can only imagine what a group like that would do if in possession of such a weapon,” Power said, referring to the militant group by one of its known acronyms.

She said the “Security Council intends to stay very much on top of this.”

“I want to stress that much more work still needs to be done on Syria’s chemical weapons program,” Power said. “The international community must continue to press for the resolution of all discrepancies and omissions in Syria’s original declaration.”

Copyright 2014 The Associated Press.