Chemical weapons were likely used in five out of seven attacks investigated by UN experts in Syria, where a 2½-year civil war has killed more than 100,000 people, according to the final report of a UN inquiry.
The UN investigators said the deadly nerve agent sarin was likely used in four of the incidents, in one case on a large scale.
The report noted that in several cases the victims included government 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 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 investigation found likely use of chemical weapons in Khan al-Assal, near the northern city of Aleppo, in March; in Saraqeb, near the northern city of Idlib, in April; and in Jobar and Ashrafiat Sahnaya, near Damascus, in August.
As initially reported by Sellstrom in September, the experts found "clear and convincing" evidence that the nerve agent sarin was used on a large scale against civilians in the rebel-held Damascus suburb of Ghouta on August 21, killing hundreds of people.
In the final report on Thursday the experts said sarin had likely also been used on a small-scale in Jobar, Saraqeb and Ashrafiat Sahnaya.
The inquiry was only looking at whether chemical weapons were used, not who used them. The Syrian government and the opposition have accused each other of using chemical weapons, and both have denied it.
TOTAL 16 ALLEGATIONS
Rebels have seized all kinds of weapons from military depots across the country, according to the United Nations. Western powers say the rebels do not have access to chemical arms.
UN Secretary-General Ban Ki-moon established the Sellstrom investigation after the Syrian government wrote to him accusing the rebels of carrying out the chemical weapons attack in Khan al-Assal.
The United Nations has since received a total of 16 reports of possible chemical weapons use in Syria, mainly from the Syrian government, Britain, France and the United States. The experts looked closely at seven of those cases.
The UN experts were from the Organization for the Prohibition of Chemical Weapons (OPCW) and the World Health Organisation.
France, Britain and the United States said the technical details of Sellstrom's initial report on the August 21 attack pointed to government culpability, while Syria and Russia blamed the rebels.
Syrian President Bashar al-Assad's government agreed to destroy its chemical weapons arsenal after the August 21 Ghouta attack, which had led to threats of US air strikes. Syria also acceded to the Chemical Weapons Convention.
The UN Security Council adopted a resolution in September to enforce the deal, brokered by the United States and Russia, which requires Syria to account fully for its chemical weapons and for the arsenal to be removed and destroyed by mid-2014.
The Hague-based OPCW has been charged with supervising the elimination of Syria's chemical arsenal.