Syrian rebels attacked a key army base in the northwest province of Idlib on Friday, the last regime bastion in the region, and regime warplanes launched air raids in Damascus province, a watchdog said.

The Syrian Observatory for Human Rights said several rebel groups pounded Wadi Deif amid violent clashes on the ground while regime warplanes launched air strikes around the army base.

Two Syrian air force generals have defected from the regime of President Bashar Assad and joined opposition forces in Turkey, a diplomat said on Friday.

The generals, commanders of the Regional Air Force, have crossed the border and arrived in the town of Reylanli in southern Turkey, the Turkish diplomat told AFP on condition of anonymity.

Mustaqbal bloc head MP Fouad Saniora stressed on Friday that the March 14-led opposition had presented “serious and acceptable” proposals over the national dialogue “contrary to what the other camp is claiming.”

He said: “The March 14 camp will return to the national dialogue once Hizbullah chief Sayyed Hassan Nasrallah announces his readiness to discuss incorporating his party's arms in the Lebanese state.”

Syrian jihadist group the al-Nusra Front, blacklisted by Washington as a terror outfit, has accused the United States of seeking to keep President Bashar Assad in power.

"The continued U.S. and international support for prolonging the regime's lifespan by giving extensions (for a political transition), sending observers and trying to negotiate peace is clear to everyone," the group's leader, Abu Mohammed al-Jawlani, said in a voice recording posted online.

The families of the victims of the Tall Kalakh ambush and Islamist inmates held in Roumieh prison urged on Friday officials to exert efforts to resolve the case of their loved ones, vowing to take escalatory measures should their demands not be met.

They said during a protest in the northern city of Tripoli: “We will shut the border-crossings with Syria until this issue is resolved.”

Syrian warplanes launched air raids in Damascus province on Friday after overnight bombardments and clashes across the country, the Syrian Observatory for Human Rights watchdog said.

"The air force for the first time attacked the Assal al-Ward area in the Kalamun region, killing one civilian, wounding dozens and destroying several homes," the Britain-based group said in a statement.

Russia, the only world power with ties to the Syrian regime, on Friday urged President Bashar Assad to talk to the opposition as Moscow itself put out feelers to the rebels.

The new pressure from Russia on the Assad regime came as Moscow revved up its bid to save a tattered peace process by first hosting a top government envoy and then planning for a meeting Saturday with Syria peace mediator Lakhdar Brahimi.

Three Ambassadors left Syria via Beirut's Rafik Hariri International Airport on Thursday, Lebanon's state-run National News Agency reported.

It said Romania's envoy traveled to Bucharest via Istanbul and Russia's diplomat headed to Moscow through a stopover at Dubai airport.

Russia, one of the few powers to maintain links with the Syrian regime of President Bashar Assad, has sent an invitation for talks to the head of the opposition Syria National Coalition, a top diplomat said Friday.

Deputy Foreign Minister Mikhail Bogdanov told the RIA Novosti news agency the talks with National Coalition head Ahmed Moaz al-Khatib could take place in Moscow or a foreign location like Geneva or Cairo.

Endless supplies of cigarettes, a BMW or Mercedes for between $4,000 and $6,000 but fuel at vastly inflated prices -- the black market is thriving on the Syria-Turkey border.

"It is all legal," insists Abu Ahmad, once a grocer in Syria's war-ravaged city of Aleppo who is now dealing in motor vehicles in the rebel-held town of Aazaz near the frontier.