At least 17 people were killed across Syria on Saturday, activists said, as an Arab League deadline for Damascus to stop its lethal crackdown on dissent was set to expire.

Among the dead were four intelligence agents killed by gunmen who raked their car with gunfire and two mutinous soldiers who died in clashes with regular troops as the military raided the central town of Shayzar after a heavy shelling, the Syrian Observatory for Human Rights reported.

The latest blood shedding came just hours before the 2200 GMT deadline from the Arab League as world pressure mounted onPresident Bashar al-Assad's regime to stop the violence which the UN says has killed more than 3,500 people since mid-March.

With rebel troops inflicting mounting losses on the regular army, Turkey and the United States both raised the spectre of civil war and Russia called for restraint.

After talks with Russian Prime Minister Vladimir Putin in Moscow, French Prime Minister Francois Fillon said: "It is indispensable to increase international pressure.

"We have tabled a resolution at the United Nations. We hope it will find as wide support as possible."

Russia has staunchly resisted any attempt to internationalise the crisis, fearing it could clear the way for a Libya-style military intervention under a UN mandate.

In October, both Russia and China vetoed a Western-drafted UN Security Council resolution that would have threatened Assad's regime with "targeted measures" over its crackdown.

"We are calling for restraint and caution. This is our position," Putin said a day after after his foreign minister, Sergei Lavrov, had likened the situation in Syria to a civil war.

US Secretary of State Hillary Clinton and Turkish Foreign Minister Ahmet Davutoglu both warned that the risk of civil war was real, amid growing losses among regular troops at the hands of mutineers.

"I say there is a risk of transforming into civil war," Davutoglu told AFP, pointing to the upsurge in attacks by army defectors.

Clinton told NBC news: "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."

Israeli Defence Minister Ehud Barak said he believed the Assad regime had reached "a point of no return" and that there could be a change of regime within months.

"I think that he went beyond the point of no return, no way that he will he resume his authority or legitimacy," Barak told a defence summit in Canada.

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.

Syria has been told by its Arab peers to stop the lethal repression against protesters by midnight (2200 GMT) on Saturday or risk sanctions, and the Arab League has already suspended it from the 22-member bloc.

As the clock ticked, there was further bloodshed in Syria and troops pressed on with their repression, activists said.

The Syrian Observatory for Human Rights said 11 civilians were killed in violence on Saturday, seven of them in Kfar Kharim in Idlib province in the northwest, close to the Turkish border.

It quoted a mutinous officer as saying that two army deserters "were killed in clashes with regular troops in Qusayr" in the restive central Homs province.

Also in central Syria "deserters raked with gunfire a car carrying four members of the air force intellience near the village of Al-Mukhtara on the Salmiyeh-Homs road killing everyone on board," the Britain-based watchdog said.

Earlier, troops stormed the central town of Shayzar, the Local Coordination Committees, an opposition umbrella group, reported.

On Friday, government forces killed at least 15 people as protesters defied a massive security force presence to urge nations to expel Syrian ambassadors to further isolate Damascus, activists said.

The Organisation of the Islamic Cooperation said it will convene an emergency meeting next Saturday at its Saudi headquarters to urge Syria to "end the bloodshed."

OIC chief Ekmeleddin Ihsanoglu said he "rejects foreign intervention in Syria" but warned that further unrest theatens regional stability as well.

Elsewhere, dozens of people rallied outside the US consulate in west Jerusalem in support of the Assad regime, denouncing what they called a "conspiracy" against Syria.