Russia's President Vladimir Putin says he is "confident" Syria's chemical weapons can be destroyed under a US-Russian plan, but not "100% sure".
Speaking to reporters he reiterated Moscow's view that the opposition may have carried out last month's deadly attack in the Damascus suburbs.
President Bashar al-Assad has warned it could take about a year to destroy Syria's chemical stockpiles.
The disarmament plan was unveiled by the US and Russia last weekend.
The West wants the deal enshrined in a UN resolution backed by the threat of military force, but Russia - Syria's ally - objects.
Addressing a meeting of the Valdai International Discussion Club in Russia's north-western Novgorod region, Mr Putin pointed out that Syria had already made steps to join the international Chemical Weapons Convention.
"These are practical steps which the Syrian government has already made," he said.
"Whether we will manage to see everything through, I cannot say 100%. But everything that we have seen up to now, in recent days, inspires confidence that this is possible and that it will be done."
President Putin insisted it was not proven that the Syrian government was behind the chemical weapons attack in the Damascus suburb of Ghouta that killed hundreds of people in August.
"It is clear that (chemical) arms were used... it's just not clear who did it," he said, adding: "We have every reason to believe that it was a provocation."
Damascus - backed by Moscow - has insisted that rebel forces carried out last month's attack.
In an earlier interview with Fox News, Mr Assad said the issue of destroying Syria's stockpiles of chemical weapons was "a very complicated operation, technically".
"And it needs a lot of money, some estimates (say) about a billion [dollars].
"So it depends, you have to ask the experts what they mean by quickly. It has a certain schedule. It needs a year, or maybe a little bit more."
Russia's Deputy Foreign Minister Sergei Ryabkov said on Wednesday that President Assad was "very serious" about the disarmament plan.
After talks in Syria, he said Damascus would fulfil its commitment to eliminate its chemical weapons by mid-2014.
Meanwhile, members of the world's chemical weapons watchdog are due to meet on Sunday to discuss the first steps in securing and destroying the Syrian arsenal, AP news agency reported.
Michael Luhan, spokesman for the Organisation for the Prohibition of Chemical Weapons, said the group's executive council would debate the US-Russian plan.
In another development, evidence has emerged of further infighting among rebel groups in Syria.
In the town of Azaz, near the Turkish border, jihadists from the al-Qaeda-linked group the Islamic State in Iraq and Syria (Isis), reportedly clashed with fighters from the Western-backed Free Syrian Army (FSA).
Activists said that Isis fighters had overrun the town in what is believed to be one of the biggest confrontations so far between the jihadists and the FSA.
The UK-based pro-opposition group the Syrian Observatory for Human Rights said the clashes erupted after a failed attempt to kidnap a German doctor working in the area.
Turkey closed one of its border gates near Azaz in response to the fighting, Reuters reported.
More than 100,000 people have been killed since Syria's civil war began in early 2011, according to the UN.
Millions have fled the country and millions more have been left homeless.