Former scientist for country’s programme says the regime used sarin agent in small quantities to halt rebel advances.
Russia says the Syrian government has agreed, “in principle”, to attend an international peace conference proposed by Russia and the US, and criticised what it called attempts to undermine peace efforts.
The summit has been suggested by the US and Russia and could take place in the Swiss city of Geneva.
“We note with satisfaction that we have received an agreement in principle from Damascus to attend the international conference, in the interest of Syrians themselves finding a political path to resolve the conflict, which is ruinous for the nation and region,” Alexander Lukashevich, Russian foreign ministry spokesman, said on Friday.
The statement was followed by an announcement of a meeting between US Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov in Paris on Monday, where they will continue discussions about the peace conference.
French Foreign Minister Laurent Fabius is also expected to join that meeting.
Faisal Mekdad, Syrian deputy foreign minister, said after talks in Moscow on Wednesday the government would soon decide whether to take part in the conference aimed at bringing government and opposition representatives together for talks.
Lukashevich said international action including a May 15 UN General Assembly resolution that praised the opposition and condemned President Bashar al-Assad’s forces has “essentially pushed [the opposition]to reject negotiations”.
Some European media have reported that the conference has been tentatively scheduled to be held on June 10.
But Lukashevich said such reports “cannot be taken seriously” because the ranks of Syrian President Bashar al-Assad’s foes remain so divided.
“Demands to immediately name a specific date for the conference without having clarity about who, and with what authority, will speak in the name of the opposition, cannot be taken seriously,” Lukashevich said.
The opposition Syrian National Coalition, which is currently meeting in Istanbul to discuss an interim government, has said it will only go to “Geneva II” if Assad steps down as president.
Louai Safi, a senior member of Syria’s main opposition, told Al Jazeera, “The fact that it has been announced in Moscow, rather than in Damascus, is a worrying point, as we want to hear the spokesperson of the Syrian government making that statement with clarity.”
“There is alot of ambiguity. What does it mean, ‘in principle’?,” he said.
“We want to hear definitive answers….We want to see a clarity of the purpose of Geneva.”
Failed first meeting
The Syrian National Coalition, which is main opposition group based outside the country, entered a second day of talks on Friday aimed at finding an approach to the joint Russian-US peace push.
The first Geneva meeting in June last year ended in a broad agreement aimed at forming a transition government in Syria and introducing a long-lasting truce.
But the deal was never implemented because of disagreements over Assad’s role in the new government and neither side’s decision to lay down their arms.
Al Jazeera’s James Bays, reporting from the United Nations. said: “The conference is likely to last three days and comes ahead of the G8 meeting in Ireland. If there are any failures at the Syria peace conference, [world leaders] can pick up the pieces there.”
He also said increased violence in Syria seen recently is “partly because of the talk of peace talks. The government side is trying to make a land grab before the meeting.”