Russia's Foreign Minister has said the situation in Syria is beginning to resemble civil war after defected soldiers attacked a key army base.
Sergei Lavrov said the Arab League must call on all sides to end the violence.Last month Moscow vetoed a UN resolution condemning the violence and called for dialogue between the government and opposition groups.
The League's 22 members said Syria must allow in a team of international monitors or face sanctions.
The plan drawn up by the Arab League earlier this month calls on Syria to withdraw tanks from restive cities, cease its attacks on protesters and engage in dialogue with the opposition within two weeks.
Mr Assad had agreed to the plan, but has failed to honour it and the violence has continued.
France's Foreign Minister Alain Juppe is heading for Turkey for talks on how to address the growing crisis.
More than 370 people have been killed since the announcement of the Arab League initiative on 2 November, say rights groups, in what appears to be the bloodiest month in the eight-month uprising.
The UN says more than 3,500 people have died since protests started in March. Syrian authorities blame the violence on armed gangs and militants.
The Syrian government has severely restricted access for foreign journalists, and reports are difficult to verify.
On Wednesday, a group of defected soldiers known as the Free Syrian Army (FSA) were reported to have launched an attack on the notorious Air Force Intelligence building in the Damascus suburb of Harasta.
The exact details of the attack were unclear, but unconfirmed reports said six government soldiers were killed.
The FSA has launched a number of other attacks and ambushes in recent weeks, but correspondents say the Harasta was their highest profile operation.
Mr Lavrov told Russian media: "We see television reports that say some new force, the so-called Free Syrian Army I believe, organised an attack on a government building."
"This is already completely similar to real civil war," he said."It is necessary to stop violence no matter where it comes from. It is an important thing because violence in Syria comes not only from government structures."
Members of the Syrian National Council (SNC) opposition coalition who travelled to Moscow earlier this week failed to convince Russia to back calls for Mr Assad to stand down.
The Kremlin instead urged the GNC to start a dialogue with Mr Assad's government, something SNC officials have said they will not do, blaming Mr Assad for the bloodshed.
A number of countries have now withdrawn their ambassadors from Syria, and its diplomatic isolation is growing over its bloody eight-month crackdown on anti-government unrest.
'End of the line'
Turkey, which shares a long border with Syria, has been increasingly critical of Mr Assad.The CA's Jonathan Head in Ankara says Turkey and France have not always seen eye-to-eye during the Arab Spring uprisings but will use Mr Juppe's visit to present Syria with incontrovertible proof that it is now almost totally isolated.
He and Turkish officials are expected to discuss ways in which the international community can increase its pressure on President Bashar al-Assad to stand down, and to begin planning for the post-Assad era.
They will also discuss ways in which the issue can be pushed at the UN Security Council, after Russia and China vetoed a resolution backing the use of "targeted measures" against Syria if the clampdown continued.
Speaking to French parliament on Wednesday, Mr Juppe warned that "the vice is tightening" around the Syrian regime.
"The Syrian people will win their fight and France will continue to do everything to help them," he said.
France, Britain, Germany and a number of Arab states are to submit a draft resolution to the calling for a vote in the UN General Assembly condemning the violence.
The Free Syrian Army commander, Riad al-Asad, told the CA on Wednesday that while he did not want people to take up arms against the regime, "It is our right to defend our people because the international community does nothing".
"I believe that with the support of the Syrian people, we can stand to challenge Bashar al-Assad, who is supported by gangs and militia," he said,
He called on countries to provide his forces with weapons, saying he believed they could "topple the regime very soon".