Monday’s UN inspectors’ report on the alleged chemical weapons attack outside Damascus will confirm that poison gas was used, according to UN Secretary General Ban Ki-moon.
Mr Moon said also today that the Syrian government had committed crimes against humanity.
Channel 4 News International Editor Lindsey Hilsum told Jon Snow that while nobody was saying the Syrian rebels had not committed war crimes, the Syrian government is in the frame at the moment “for these extraordinary atrocities”.
“That is why Sergei Lavrov and John Kerry, the Russian and the American envoy, understand that the talks in Geneva cannot just be about chemical weapons.
Today Messrs Kerry and Lavrov, in Geneva, also met with UN-Arab League envoy Lakhdar Brahimi to push for a new international peace conference to support the creation of Syrian transitional government.
Mr Kerry said: “We are committed to try to work together, beginning with this initiative on the chemical weapons in hopes that those efforts could pay off and bring peace and stability to a war-torn part of the world.”
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Mr Kerry, who said the ongoing talks on chemical weapons were “constructive”, said that he and Mr Lavrov planned to meet in New York later this month and hoped to agree a date for a Geneva peace conference.
He added: “I think we would both agree that we had constructive conversations regarding that but those conversations are continuing and both of us want to get back to them now.”
Syria’s ambassador to the United Nations said that as of Thursday his country had become a full member of the treaty, which requires destruction of all chemical weapons.
Syria made a formal bid to join the Chemical Weapons Convention. The UN welcomed the move, but said that it could take 30 days for Syria to become a member.
Mr Lavrov said Russian and US experts needed to engage with the UN Organisation for the Prohibition of Chemical Weapons to design a roadmap to resolve the issue as soon as practical.
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He said: “We are here basically to discuss the issue of chemical weapons in Syria, now that the Assad government joined the chemical weapons convention.
“We have to engage our professionals together with the chemical weapons prohibition organisation as we agreed with the United Nations, to design a road which could make sure that this issue is resolved quickly, professionally, as soon as practical.”
Mr Kerry cautioned after meeting Mr Lavrov on Thursday that the United States could still carry out a threat to attack President Bashar al-Assad in retaliation for a poison gas attack last month if Washington was not satisfied with Syria’s response.
Mr Brahimi said working to remove chemical weapons from Syria would form an important element in efforts to hold new peace talks, following an earlier failed attempt at Geneva last year.
Speaking at a summit of an international security grouping in Kyrgystan, President Putin said the move by Syria to join the convention showed that the nation has “serious intentions to follow this path”.
“I would like to voice hope that this will mark a serious step toward the settlement of the Syrian crisis,” Putin said.
“As you know the initiative to establish international control over Syria’s chemical weapons is underway and we attach much significance to it and hope for positive results which should lead to a peaceful – at least creating conditions for – a peaceful settlement of the Syrian crisis.”
The talks were the latest in a rapidly moving series of events following the alleged 21 August gas attack on suburbs in Damascus.
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The US blames Syrian President Bashar al-Assad for the use of chemical weapons, although the president denies his government was involved and instead points to rebels engaged in a two-year-old civil war against his government.
US President Barack Obama began building a case for support at home and abroad for a punitive military strike on President Assad’s forces, then changed course and asked congress to give him explicit authority for a limited strike.
With the campaign for congress building to a vote one that he might well lose, President Obama on Tuesday said he would consider a Russian proposal calling for international control of President Assad’s chemical weapons and their eventual destruction.