Russia is "open to constructive proposals" on Syria but remains opposed to any UN move backing previously approved unilateral sanctions or the use of force, Foreign Minister Sergei Lavrov said Wednesday.

"We are open to constructive proposals that go in line with the set task of ending the violence," he said, but any new UN action could not justify force or "sanctions that were declared without any consultations with Russia or China."

Syria has agreed to extend a widely criticised Arab League observer mission for a second month, just hours after launching an angry tirade against the bloc's efforts to mediate in the crisis.

Muallem said Syria had no choice but to confront the armed groups that the government holds responsible for the violence which the UN says has killed more than 5,400 people since March, stressing that Russia would never accept foreign intervention.

The US State Department said US and Russian diplomats held "very constructive" talks this week in Moscow amid efforts to resolve their differences in the global response to unrest in Syria.

"I wouldn't say that there was a major breakthrough. But I think walking through how we understand the situation on the ground, how the Russians see it... and then beginning to strengthen and deepen our conversation about where we go next in the UN Security Council, was very useful," US State Department spokeswoman Victoria Nuland said.

Washington is calling for Bashar Al-Assad's resignation while the Russians continue to support him.

Western governments have been capitalising on the Arab League's tough new stance to embark on a fresh drive for action by the UN Security Council after previous efforts were blocked by Beijing and Moscow.

Britain, France, Germany and Arab nations are working on the resolution which could face Russian opposition because of a call on all UN member states to follow Arab League sanctions against Assad's regime.

Diplomats from several Security Council and Arab nations said there could a vote as early as Monday or Tuesday next week.

Moscow, a Cold War ally of Damascus which retains a naval base at Tartus on Syria's Mediterranean coast, has spoken out strongly against sanctions.

Russia and China vetoed a previous European attempt in October to get a resolution passed condemning Assad for the violence.