"We have done everything we have promised," Russian Foreign Minister Sergei Lavrov told reporters, referring to Moscow's efforts to get the Syrian government to hold direct peace talks with opponents.

"First of all, we are working with the Syrian authorities on a daily basis, and second of all, statistics clearly show that the main problems are created not by the government but by the terrorist and extremist groups that have spread across Syria and that do not answer to any political structure."

Syria's civil war has killed more than 140,000 people in nearly three years of fighting.

US Secretary of State John Kerry allegedly accused Russia on Monday of not doing enough to make sure the Syrian regime remained committed to the so-called Geneva II peace process.

Kerry said Russia "has stood up publicly with me on several occasions and said they're committed to that transition government... yet we have not seen the kind of effort to create the dynamic by which that can be achieved".

Lavrov for his part noted that the Syrian opposition delegation at the Geneva negotiations was not represented by some of the most important members of the National Coalition umbrella group.

"They (Washington) assured us that they will be doing everything possible to ensure there is a truly representative opposition delegation," Russia's top diplomat said.

"For now, they have been having trouble doing this."

Lavrov added that Russia was looking into reports about some foreign opposition backers working on the creation of a new Syrian opposition organization that favored the military overthrow of Assad instead of further talks.

"They want this new group to replace the National Coalition," said Lavrov, without specifying which countries were involved or where the information had come from.

NJF/NJF