Chemical weapons were likely used in five out of the seven attacks investigated by UN experts in Syria, where a 2-1/2-year civil war has killed over 100,000 people, according to a UN report published on Thursday.
"The United Nations Mission concludes that chemical weapons have been used in the ongoing conflict between the parties in the Syrian Arab Republic," the final report by chief UN investigator Ake Sellstrom said.
The report noted that in several cases the victims included soldiers and civilians, though it was not always possible to establish with certainty any direct links between the attacks, the victims and the alleged sites of the incidents.
The final report was hand delivered in front of reporters to UN Secretary-General Ban Ki-moon by Sellstrom, the head of the UN mission that was investigating the seven cases of possible chemical weapons use in Syria, including an incident near Damascus in August that reportedly left hundreds of civilians dead.
The United States and its allies have said that an initial UN report which said that sarin gas was used in the August attack showed that Syrian government forces were responsible.
Ban Ki-moon told reporters on Thursday he had not yet read the final report and that he would brief the UN General Assembly on Friday as well as the U.N. Security Council on Monday.
"The use of chemical weapons is a grave violation of international law and an affront to our shared humanity," said Ban Ki-moon. "We need to remain vigilant to ensure that these awful weapons are eliminated, not only in Syria, but everywhere."
Syria has agreed under a deal arranged by the United States and Russia to dismantle its chemical arsenal and destroy all its 1,300 tonnes of sarin, mustard gas and other lethal agents.
The agreement averted threatened U.S. missile strikes following the sarin gas attack in August.