A fact-finding mission by the UN chemical weapons watchdog has found that some people in Syria may have been exposed to sarin or a sarin-like gas, according to a report released Monday.

The mission by the Hague-based Organisation for the Prohibition of Chemical Weapons (OPCW) said it was investigating 11 incidents of the use of toxic chemicals reported by the Syrian government.

The report did not say when the 11 incidents took place or specify any location.

"In one instance, the analysis of some blood samples indicates that individuals were at some point exposed to sarin or a sarin-like substance," said the OPCW report sent to the Security Council last week.

"Further investigation would be necessary to determine when or under what circumstances such exposure might have occurred," said the report.

Previous fact-finding missions by the OPCW in Syria have pointed to the use of chlorine and mustard gas.

The UN Security Council is due to discuss Syria's chemical weapons use during a meeting on Tuesday.

President Bashar al-Assad's regime and rebel forces have accused each other of using chemical agents in the nearly five-year war that has killed more than 250,000 people.

After an August 2013 sarin attack outside Damascus that much of the international community blamed on Assad's government, the regime agreed to turn over its chemical arsenal.

The report said that 99.6 percent of all declared chemical weapons in Syria had been destroyed.