"The conclusion is that chemical weapons have been used in the ongoing conflict between the parties in the Syrian Arab Republic... Against civilians including children on a relatively large scale," said the report.
The report submitted by the UN inspectors probing the use of chemical weapons in Syria at 14 instances was submitted to UN chief Ban Ki-moon who will present it before a close door session of Security Council today.
"The environmental, chemical and medical samples we have collected provide clear and convincing evidence that surface-to-surface rockets containing the nerve agent sarin were used... In the Ghouta area of Damascus" on 21 August, said the report which was inadvertently leaked.
Syrian opposition and the West have accused President Bashar Al-Assad's forces of using chemical weapons on August 21 in a Damascus suburb that reportedly killed hundreds, a charge denied by the government.
The government instead blamed the rebels for carrying out chemical attacks in Damascus and other parts of the country during the over two and half year long civil war that has left more than 100,000 people dead and forced millions to leave the country.