Syrian rebels launched a devastating car bomb attack Monday that killed 50 pro-regime fighters, a watchdog said, as air strikes pounded rebel positions and the opposition held talks on an overhaul.

The suicide car bomb attack on a military post in the central province of Hama struck early Monday, killing at least 50 government troops and loyalist militiamen, the Syrian Observatory for Human Rights said.

The attack was one of the deadliest on pro-regime forces since the start of the uprising against President Bashar al-Assad's rule in March last year.

State television and the Britain-based Observatory said a car bomb attack had also killed 11 people and wounded dozens in the west Damascus district of Mazzeh, home to many embassies and state security offices.

Regime aircraft meanwhile continued to pound rebel-held positions around the country, with one air strike killing at least 22 rebel fighters in the town of Harem in the northwestern province of Idlib, the Observatory said.

The rebels have scored significant gains in recent weeks and hold swathes of territory in the north, but have come under intense bombardment from the air as Assad's regime seeks to reverse its losses.

An air strike in the Idlib province town of Kafr Nabal killed 15 civilians, the Observatory said, with a video posted online by activists showing rescuers carrying blood-soaked bodies amid burning cars and uprooted trees.

"Bashar, even if you kill us all, we will stay determined to bring you down!" one man shouts in the video.

Fighting also erupted in southern districts of the capital on the edge of the Yarmuk Palestinian refugee camp, the Observatory said, with Palestinian sources saying 31 people had died from shelling at the camp on Sunday and Monday.

In second city Aleppo, fighting broke out at a roundabout at the northwestern entrance to the city in Zahraa district and on the airport road to the southeast, the Observatory and residents said.

Nationwide, at least 192 people were killed in Monday's violence, the Observatory said, 53 civilians, 85 soldiers and 54 rebels.

The bloodshed added urgency to a meeting of the Syrian National Council in Qatar, where the United States is reportedly pressing for a new umbrella organisation to unite the fractured opposition.

According to the reports, which emerged after US Secretary of State Hillary Clinton said the SNC was not representative, long-time dissident Riad Seif is touted as the potential head of a new government-in-exile dubbed the Syrian National Initiative.

Seif on Sunday denied planning to head such a government, while SNC chief Abdel Basset Sayda denounced what he called "efforts to bypass the SNC".

On Monday, SNC members approved a restructuring that will see the organisation add 200 new members representing 13 different political groups.

On Tuesday, SNC members will debate a proposal put forward by Seif to create a new political body to represent the opposition, folding in the SNC and other anti-regime groups.

Washington said it was waiting to see which groups would actually be invited to join the new body.

"Just broadening the numbers doesn't necessarily broaden the representation, so we think we have to see who they actually bring into the group," State Department spokeswoman Victoria Nuland told reporters.

Russian Foreign Minister Sergei Lavrov accused countries that support the rebels of encouraging them to fight rather than pressuring them to negotiate.

Russia, one of the Syrian regime's most influential allies, held no sway over the rebels, Lavrov said in Cairo.

Countries with influence over the rebels, among them some Gulf Arab states and Western powers such as the United States, should encourage them to "sit at the negotiating table," Lavrov said.

Some of those countries prefer to "unify the rebels not on the basis of negotiations but on the basis of continuing the fighting," he said.

Gunfire from the Syrian side of the armistice line hit an Israeli military vehicle in the the occupied Golan Heights on Monday, the Israeli army said.

"Apparently they were stray bullets, and there were no injuries," military spokesman told AFP.

Israel's armed forces chief Lieutenant General Benny Gantz said on Sunday that his country could become involved in the Syrian conflict, as fighting between regime forces and rebels raged near Israeli positions on the Golan.

The Observatory says more than 36,000 people have died since the uprising against Assad's rule broke out, first as a protest movement inspired by the Arab Spring and then as an armed rebellion.

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