Turkish Prime Minister Tayyip Erdogan on Tuesday warned Syrian President Bashar Assad his government was on a "knife-edge" and demanded an immediate apology after attacks on Turkey's diplomatic missions in Syria.

Meanwhile, also on Tuesday, Russia urged opponents of Assad to hold talks with the government, hoping to secure a peaceful resolution to months of violence without abandoning its support for the isolated leader.

"Nobody now expects the (Syrian) people's demands to be met. We all want the Syrian administration, which is now on a knife-edge, to turn back from the edge of the cliff," Erdogan told a party meeting.

Turkey, after long courting Assad, has lost patience with its neighbor's failure to end an eight-month crackdown and implement promised democratic reforms.

Turkey now hosts the main Syrian opposition and has given refuge to defecting Syrian soldiers. On Tuesday, Erdogan praised an Arab League decision to suspend Syria.

Underlining how much ties between the two powers have deteriorated, protesters armed with sticks and stones attacked Turkish diplomatic missions in Syria over the weekend, burning the Turkish red and white flag.

Syrian Foreign Minister Walid al-Moualem apologised on Monday for the attacks, which also included raids on Saudi and French missions. But Erdogan said Turkey expected a further expression of apology although he did not elaborate.

"I once again strongly condemn the attacks on Turkish officials and on the Turkish flag. We expect the Syrian administration to undertake immediately all the necessary steps to apologize and take responsibility," Erdogan said.

"Bashar, you are required to punish those who attacked the Turkish flag. We want the Syrian administration to not only respect the Turks in Turkey and the Turkish flag but also to respect their own people, we especially want this."

In high-level talks in Moscow, the main Syrian National Council opposition group responded by urging Russia to join growing international calls for Assad to step down, Russia's Interfax news agency reported.

Syrian National Council head Burhan Ghalioun, however, said Russia and the international community should first send "an important signal and demand the resignation of Bashar Assad," Interfax reported.

In meetings with the delegation, senior Russian diplomats urged "all Syrian opposition groups that reject violence ... to immediately join in the realization of the Arab League initiative to resolve the crisis in Syria through the launch of dialogue between the Syrian authorities and the opposition," the Foreign Ministry said.

Russia joined China last month in a double veto of a UN Security Council resolution that would have condemned Syria's bloody crackdown on pro-democracy protesters, and has accused the West of discouraging dialogue between Assad and his opponents.