Syrian President Bashar al-Assad defiantly vowed to fight and die if needed as an Arab League deadline for his government to stop its lethal crackdown on protesters expired with 17 more people killed.

Among the dead from Saturday were four intelligence agents killed by gunmen who raked their car with gunfire, and two mutinous soldiers who died in clashes with regular troops in the central town of Shayzar, rights campaigners said.

The latest bloodletting added to the more than 3,500 killed since mid-March, and came just hours before the passing of Saturday's midnight (2200 GMT) deadline from the Arab League for Assad to end the crackdown or face sanctions.

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.

But in an interview with London's Sunday Times, conducted before the Arab League deadline lapsed, Assad said he was ‘definitely’ prepared to fight and die for Syria if faced with foreign intervention.

"This goes without saying and is an absolute," he said.

The president said he felt sorrow for each drop of Syrian blood spilt but insisted Damascus must go after armed rebel gangs and enforce law and order.

"The conflict will continue and the pressure to subjugate Syria will continue," he said. "I assure you that Syria will not bow down and that it will continue to resist the pressure being imposed on it."

Assad accused the Arab League of creating a pretext for Western military intervention, which he said would trigger an ‘earthquake’ across the Middle East.

But 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 invoke international involvement in the crisis, fearing it could clear the way for a Libya-style military campaign under a UN mandate.

"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, and Israeli Defence Minister Ehud Barak said he felt Assad had reached "a point of no return" with a change of regime possible within months.

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."

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.

With the peace deal in tatters, the Arab League has already suspended Syria from the 22-member bloc and saw its deadline expire on Saturday with no compliance from Assad's security forces.

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.

The Britain-based watchdog quoted a mutinous officer as saying that two army deserters "were killed in clashes with regular troops in Qusayr" in the restive central province of Homs.

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

That came after pro-Assad troops stormed the central town of Shayzar, according to the Local Coordination Committees, an opposition umbrella group.

The 57-nation Organisation of Islamic Cooperation said it would convene an emergency meeting next Saturday at its Saudi headquarters to urge Syria to "end the bloodshed".

The OIC ‘rejects foreign intervention in Syria’, its chief Ekmeleddin Ihsanoglu said, but he warned that further unrest threatened regional stability as well.