There is “clear and convincing evidence” that chemical weapons were used in the August 21 attack in Syria, UN inspectors said in their report on Monday.

“The conclusion is that chemical weapons have been used in the ongoing conflict between the parties in the Syrian Arab Republic, also against civilians, including children, on a relatively large scale,” said the report, which was submitted to the UN Security Council in New York.

The report said surface-to-air rockets containing the nerve gas sarin were used in Ein Tarma, Moadamiyan and Zamalka in the Ghouta area of Damascus. It does not say which parties in the conflict used the weapons.

Its publication came as the United States, France and Britain were demanding a strong UN resolution to implement a U.S.-Russian accord on dismantling Syria’s chemical weapons.

UN inspectors visited Syria last month to investigate the August attack on two Damascus suburbs, which the Syrian opposition and the United States say killed more than 1,400 people.

The regime of President Bashar al-Assad and the rebels have since blamed each other for the attacks.

UN Secretary General Ban Ki-Moon was presenting the results of the inspectors’ report in New York after briefing the Security Council.

The results of the investigation come after the weekend deal between Washington and Moscow on ridding Syria of its stockpiles of chemical weapons.

French Foreign Minister Laurent Fabius said his country, the U.S. and Britain — all veto-holding members of the UN Security Council — would push for a “strong” resolution with “serious consequences” in the event of non—compliance by Mr. al-Assad’s regime.

The resolution should also state clearly “that those responsible for crimes committed should be held to account,” said Mr. Fabius after talks in Paris with US Secretary of State John Kerry and British Foreign Secretary William Hague.

Mr. Kerry said the resolution should employ the “strongest, most forceful terms possible”. “If the Assad regime believes this is not enforceable and we are not serious they will play games,” said Mr. Kerry, who negotiated the deal with his Russian counterpart, Sergei Lavrov.

The agreement, which has averted the threat of imminent U.S. military strikes against Syria, requires Damascus to declare its stock of chemical weapons by the end of this week, and give up that arsenal by mid-2014.

“If Assad fails to comply with the terms of this framework agreement, make no mistake, we are all agreed — that includes Russia — that there will be consequences,” Mr. Kerry said.

But Mr. Lavrov said on Monday in Moscow that the UN resolution would not mention the threat of force.

He said the U.S. had wanted the resolution to include the possibility of the use of force under Chapter VII of the UN Charter.

“But the document that we approved and that binds our leaders to act accordingly, contains no mention of that,” he was quoted as saying by the Interfax news agency.

French diplomats say that a report that indirectly incriminates Mr. al-Assad would strengthen the hand of the U.S., Britain and France in demanding a tough UN resolution under Chapter VII.

Chapter VII carries the threat of punitive action, ranging from sanctions up to force, in the event of non-compliance. But the diplomats said there was no automatic punishment mechanism in a draft resolution put forward by France and that any breaches would likely require another UN resolution.

A Syrian minister at the weekend hailed the deal as a “victory for Syria”, but Mr. Kerry said that lifting the threat of immediate military action did not mean the U.S. was content to let Mr. al-Assad remain in power.

The military wing of the main opposition Syrian National Council has rejected the deal, saying it lets Mr. al-Assad off the hook for the August 21 chemical attack.

Meanwhile, Iran, a strong backer of the Syrian regime, said it would be prepared to accept a leader other than Mr. al-Assad.

The priority is for Syria to return to stability, Iranian President Hassan Rouhani said. “Then we would accept whoever the majority of Syrian people vote for in an election,” he said, according to the Fars news agency.

In Geneva, the UN’s chief human rights investigator on Syria reminded the UN Human Rights Council that “the vast majority of the conflict’s casualties result from unlawful attacks using conventional weapons such as guns and mortars,” rather than chemical weapons.

Since July, the government has continued its heavy bombing and shelling campaigns across the country, said Paulo Sergio Pinheiro, who heads the Commission of Inquiry on Syria.

Government forces used cluster munitions, while an incendiary bomb dropped on a school in August killed eight students and inflicted life-threatening burns on 50 others.

According to UN figures, more than 100,000 people have been killed since March 2011, when peaceful protests against Mr. al-Assad’s regime were repressed by force and quickly descended into civil war.

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