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.
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The report also for the first time documented the systematic imposition of sieges and forcible displacement.
"Government and affiliated militia have systematically employed sieges across the country, trapping civilians in their homes by controlling the supply of food, water, medicine and electricity," it said.
"In some instances, anti-government armed groups have also employed this tactic," said the report.
The report also said that the tragedy of Syria's 4.25 million internally displaced persons was "compounded by recent incidents of IDPs being targeted and forcibly displaced".
It pointed out that both sides have committed war crimes, however, "the violations and abuses committed by anti-government armed groups did not reach the intensity and scale of those committed by government forces and affiliated militia".
"This is a disparity in intensity. It is not the disparity in the very nature of the crimes and violations. They are the same. For us, the only thing that accounts is the act of committing these violations," said Pinheiro.