The report has been prepared by chemical weapons specialists and doctors who traveled to Syria to conduct interviews and collect samples amid the fighting.

It was the first time the United Nations asserted as fact that chemical weapons had been used on multiple occasions in the fighting between the Syrian forces and the insurgents seeking to topple President Bashar al-Assad, including chemical weapons use after world outrage over the alleged Aug. 21 attack, which killed hundreds of people. Syrian government has blamed foregin-backed militants for the attack.

A preliminary version of the report, which was released on Sept. 16 and focused only on the Aug. 21 attack near Damascus, played a role in developments that ultimately led to an agreement in which the Syrian government pledged to destroy all of its chemical munitions.

The destruction, which the United Nations is helping to oversee, has been proceeding for two months and is considered a conspicuous success in what is an increasingly grim conflict that has claimed more than 100,000 lives.

“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 United Nations report stated.

Secretary General Ban Ki-moon received the final version on Thursday and made it public a few hours later.

The authors, members of a panel led by the Swedish scientist Ake Sellstrom, studiously avoided saying who was responsible in any of the attacks, saying it was their mandate only to ascertain whether they had taken place.

Syria insisted that chemical weapons had been used against its soldiers after the Aug. 21 attack. The report said there was evidence supporting “the probable use of chemical weapons” in two episodes in the Damascus area — in Jobar on Aug. 24 and Ashrafiah Sahnaya on Aug. 25. In both cases, the report said, chemical weapons may have been used on “a relatively small scale against soldiers.”

BA/BA