UNITED NATIONS — The head of the mission charged with destroying Syria's chemical weapons says the last 16 containers of chemical agents awaiting transport out of the country are in a contested area near Damascus that is currently inaccessible.

Sigrid Kaag told reporters after briefing the U.N. Security Council on Thursday that it's not possible to arrange a cease-fire so authorities can get to the site where five containers of the most dangerous chemicals and 11 containers of less toxic chemicals — representing 8 percent of Syria's declared stockpile — are awaiting removal.

Syria missed an April 27 deadline for all chemical agents to be removed or destroyed in the country.

Kaag appealed to countries with influence on the armed groups to ensure unfettered access so the 16 containers can be removed.