There are "reasonable grounds" to believe that chemical agents have been used as weapons in Syria, the report of the International Commission of Inquiry on Syria said Tuesday.

"In four attacks, there are reasonable grounds to believe that limited quantities of toxic chemicals were used," said the report, presented by the commission chair Paulo Pinheiro to the Human Rights Council's 23rd session.

However, the report, which covered the period from January 15 to May 15, said "it has not been possible, on the evidence available, to determine the precise chemical agents used, their delivery systems or the perpetrator".

"Other incidents also remain under investigation," it said.

It said that Syrian government possesses a number of chemical weapons, while "it is possible" that anti-government armed groups may access and use chemical weapons.

Pinheiro told an embargoed press conference Monday that the findings were based on interviews with witnesses, including victims, refugees and medical staff. Endi