United Nations inspectors say there is "clear and convincing evidence" that chemical weapons were used on a relatively large scale in an attack last month in Syria that killed hundreds of people.
In a report issued Monday, inspectors said environmental, chemical and medical samples show "unequivocally and objectively" that "surface-to-surface rockets containing the nerve agent sarin were used in the Ghouta area of Damascus'' on August 21.
The report cited survivors who reported "a military attack with shelling" followed by an onset of symptoms including "blurred vision, nausea, vomiting and an eventual loss of consciousness."
Almost all of the biomedical samples examined tested positive for sarin exposure, including 93 percent collected from urine and 88 percent from blood. A majority of the rockets or rocket fragments recovered also were found to be carrying sarin.
The inspectors were charged with determining if chemical weapons were used and not who unleashed them. The U.S. says Syrian forces were behind the attack that Washington says killed more than 1,400 last month.
Syria says it was rebel fighters, not government forces, who are responsible.
U.N. chief Ban Ki-moon said Monday that the use of chemical weapons in Syria is a "war crime" and demanded the threat of sanctions to back a plan to destroy the arms.
Mr. Ban made the comments in closed consultations of the 15-nation U.N. Security Council, according to diplomats at the meeting.
In Geneva, the U.N. Commission of Inquiry on Syria said Monday it is investigating 14 alleged attacks with chemical weapons or chemical agents in Syria over the last two years. The report is expected to add momentum to a deal to eradicate Syria's chemical weapons program.
Earlier Monday, the U.S., France and Britain agreed on the need for a strong United Nations resolution that sets precise and binding deadlines for Syria to give up its chemical weapons.
British Foreign Secretary William Hague said Monday the task is difficult and complex, but stressed the need to maintain pressure on President Bashar al-Assad's government.
"It is the Assad regime that has stockpiled these weapons and that has used them repeatedly against the Syrian people, so the pressure is on them to comply with this agreement in full. The world must be prepared to hold them to account if they don't, and our three countries are certainly determined to do so."
Hague spoke alongside French Foreign Minister Laurent Fabius and U.S. Secretary of State John Kerry after they met in Paris. The talks came days after the U.S. and Russia announced a plan that calls on Syria to detail its chemical weapons stockpile. The Syrian government has promised to comply.
Kerry said Monday that anything less than full compliance by the Syrian government with a U.N. resolution would not be accepted. He also expressed the need to find a lasting solution beyond taking chemical weapons away from Mr. Assad's forces.
"We understand that removing the chemical weapons still leaves him with artillery and airplanes and he uses them indiscriminately against his people, and we are going to do everything in our power to continue to work towards the political resolution that is so critical to ending that violence."
Earlier efforts to address the Syrian crisis at the U.N. Security Council have failed, with Russia and China using their veto power to block any outside intervention.