A fact-finding mission of the global anti-chemical weapons watchdog has found indications that some people in Syria were exposed to deadly sarin gas, or a compound like it, according to a report the United Nations released on Monday.

The findings come in the latest monthly report on Syria from the Organization for the Prohibition of Chemical Weapons (OPCW) chief Ahmet Uzumcu. U.N. Secretary-General Ban Ki-moon attached it in a Dec. 29 letter to the 15-nation Security Council.

Uzumcu's report said his agency's fact-finding mission in Syria was looking into charges by the Syrian government that chemical weapons were used in 11 instances. The report did not specify when the alleged toxic gas attacks occurred.