The United Nations has confirmed that chemical weapons have been used in Syria on a large scale.
A report by UN inspectors says sarin gas was used in a rocket attack in the Syrian capital, Damascus, last month.
As expected, the report does not say who launched the attack, but it notes the weather at the time ensured the maximum number of people were killed, Reuters reports.
The United States says 1400 people died, including 400 children, in the assault on 21 August and says the Syrian regime was responsible.
"On the basis of the evidence obtained during the investigation of the Ghouta incident, the conclusion is that chemical weapons have been used in the ongoing conflict between the parties in the Syrian Arab Republic ... on a relatively large scale," said the report.
"In particular, 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," it said.
United Nations secretary-general Ban Ki-moon has described the attack as a "war crime" and says the report makes chilling reading.
"The results are overwhelming and indisputable. 85% of the blood samples tested positive for sarin. A majority of the environmental samples confirmed the use of sarin," he says.
Mr Ban is calling on the UN Security Council to impose consequences for any failure by Syria to keep to a Russia-United States plan to identify and destroy its chemical arsenal.
The White House says the report has bolstered the United States argument that the Syrian Government was responsible for the attack.
President Barack Obama's national security adviser Susan Rice says the technical evidence in it is significant - for instance, that the sarin nerve agent was high-quality and that a particular rocket was used. She says only the Syrian regime had the capability to mount such an attack.
New Zealand Foreign Affairs Minister Murray McCully says the release of the report has reaffirmed the need for the international community to respond to the crisis. He says those responsible need to be held accountable.
Mr McCully says the Government welcomes the agreement between the US and Russia for the elimination of Syria's chemical weapons and calls on all parties involved to move forward in good faith, following a quick and clear timetable.