Syrian security forces killed at least 12 civilians on Friday, including two children, on the eve of an Arab League deadline for Damascus to stop its lethal crackdown on protesters.
The latest bloodletting came as Turkey and the United States raised the risk of civil war and as thousands of protesters took to the streets to urge nations to expel Syrian ambassadors, in defiance of massive security force deployments.
Russian Prime Minister Vladimir Putin called for restraint over the Syrian crisis, after talks with his French counterpart, Francois Fillon, who accused President Bashar al-Assad of being deaf to pressure.
"We are calling for restraint and caution. This is our position," Putin told a Moscow news conference, the day after his foreign minister had likened the situation in Syria to a civil war.
Russia has been deeply opposed to Western efforts to internationalise the crisis, fearing it might clear the way for a Libya-style Western military intervention under a UN mandate.
In October, Russia and China vetoed a Western-drafted Security Council resolution that would have threatened Assad's regime with "targeted measures" over its crackdown.
Turkey said the risk of civil war was real -- a warning also echoed by analysts monitoring developments in Syria amid growing losses among regular army troops at the hands of mutinous soldiers.
The Arab League said it was examining a Syrian request to make changes to a proposal to send 500 observers to Damascus to help implement a peace deal agreed earlier this month.
Facing growing isolation, Syria has been told by its Arab peers to stop the lethal repression against protesters by 2200 GMT on Saturday or risk sanctions, and the Arab League has suspended it from the 22-member bloc.
Iran said the suspension was "a historic mistake" and would in itself cause civil war.
"The path the Arab League has taken is completely about defeating Syria from inside and triggering a civil war," Alaaddin Boroujerdi, head of the Iranian parliament's foreign policy committee, said on a visit to Turkey.
The repression against demonstrations that erupted in mid-March has claimed more than 3,500 lives, according to UN estimates.
Protesters initially took to the streets seeking democracy in one of the Arab world's most autocratic countries but now want the ouster of Assad's regime, and they have the support of much of the Western world.
French officials called for stern action.
"We think that it is indispensable to increase international pressure and we have tabled a resolution at the United Nations. We hope it will find as wide support as possible," Prime Minister Fillon said.
Foreign Minister Alain Juppe, in Turkey ahead of a tour of Arab countries, said the "time has come to increase sanctions" on Syria, branding the situation "unacceptable."
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The foreign minister of Turkey, a once close Assad ally that has become disillusioned with the regime, sounded the alarm.
"I say there is a risk of transforming into civil war," Ahmet Davutoglu told AFP, pointing to the upsurge in attacks by army defectors against key regime targets.
"It is now the right time to stop this massacre and, therefore, the Arab initiative is important," he said.
And US Secretary of State Hillary Clinton warned of the potential for civil war, either directed or influenced by army defectors.
"I think there could be a civil war with a very determined and well-armed and eventually well-financed opposition that is, if not directed by, certainly influenced by defectors from the army," she told the US television network NBC.
"We're already seeing that, something that we hate to see because we are in favour of a peaceful ... protest and non-violent opposition."
Clinton put the blame for the violence squarely on the regime, saying that the way it has responded "has provoked people into taking up arms against them."
On the ground, 12 people were killed when security forces fired on demonstrators in several restive provinces, including the flashpoint central cities of Homs and Hama.
Five of the dead, including a child, were killed outside the southern town of Daraa, cradle of the anti-regime protests.
The Syrian Observatory for Human Rights, which reported the death toll, said a 14-year-old boy was also among the dead, and said dozens of people were wounded by gunfire nationwide.
State television reported that a bomb blast in Hama killed three members of the security forces and critically wounded an officer, while state news agency SANA said two were killed.
SANA also reported that five security personnel were wounded when gunmen fired on them in Daraa, where a bomb squad defused an explosive device.
Activists called protests after the main weekly Muslim prayers to urge countries around the world to expel Syrian ambassadors.
"They are the ambassadors of crime. Expel them, O free ones," the Syrian Revolution 2011, one of the main groups behind the protests, said on Facebook.
Another umbrella group of activists, the Syrian Revolution General Commission, called for nationwide protests "until the regime falls."
But counter-rallies were held in some parts of Damascus, SANA reported, with people demonstrating against the Arab pressure on the Syrian government.