A prominent Syrian rebel leader has died from wounds suffered in an air raid on the city of Aleppo, activists have said.

It is a setback for rebels fighting against President Bashar al-Assad.

Abdel Qader Saleh, head of the Islamist al-Tawhid Brigades, which is backed by Qatar, died in a Turkish hospital.

He had been wounded on Thursday when Assad's forces raided a Tawhid meeting and killed another commander on the spot, opposition sources said.

"We declare the martyrdom of Abdel Qader Saleh," a statement by Tawhid said.

Having lost several key rebel bases in the past few weeks, the rebel leader had been working on regrouping fighters in Aleppo before he died.

Meanwhile, Assad forces have fired rocket and artillery barrages on a besieged mountain town near Lebanon.

They are pushing to capture the strategic area following advances against rebels in Damascus and in the north of Syria.

Heavy bombardments hit Qara, 80km north of Damascus in the Qalamoun mountains, as rebels hid in the rocky terrain, refugees and opposition activists said.

Located near the highway linking the capital to Aleppo, Syria's biggest city, the region has been used by rebels to cross from Lebanon.

The Danish Refugee Council, which operates on the Lebanese frontier, said there were preliminary estimates that 10,000 to 12,000 Syrians had fled the bombardment since Friday.

Hundreds of them lined up for shelter in bleak winter rain in the Lebanese border town of Arsal today.

Imposing control over the area would help link Damascus with the Mediterranean coast, potentially an important route for chemical weapons to be removed from Syria under an October deal that spared Syria from US attacks.

Diplomats have identified the road as the preferred route for the chemical arms, which pose an unprecedented challenge to dismantle in the midst of an all-out civil war.

Assad's forces have been on the offensive this year after setbacks earlier in the conflict, which began in 2011 and has killed 100,000.

His troops have made further gains and his diplomatic position has improved markedly in the weeks since the Russian-US chemical weapons deal.

Just a year ago, Western countries were predicting he would be overthrown soon.