Syrian warplanes on Sunday launched air strikes on the eastern town of Albu Kamal near the Iraqi border and pounded rebel lines near Damascus and in the northern city of Aleppo, a watchdog said.

Fighting meanwhile raged early morning around the northeast town of Ras al-Ain on the border with Turkey, the Syrian Observatory for Human Rights said.

The surge in violence follows another day of bloodletting across Syria on Saturday which saw 121 people killed, including 11 civilians in Daraya just outside the capital, the site of the worst massacre in Syria's 20-month conflict.

The Britain-based watchdog said that in eastern Syria, two civilians were killed in air raids on the town of Albu Kamal on the Iraqi border while several districts of Deir Ezzor city were shelled by tanks.

The watchdog also reported clashes between President Bashar al-Assad's forces and rebels during the night in the town of Harasta on the northeastern outskirts of Damascus.

The Local Coordination Committees, a network of opposition activists on the ground, meanwhile, reported heavy shelling overnight by regime forces on rebel areas southwest of the capital and in the town of Yabrud to the north.

In the northern city of Aleppo, where fighting between rebels and government troops has raged since mid-July, mortars rained down on the rebel bastions of Shaar in the east, Sukari in the south and Halab al-Jadida in the west, according to the Observatory.

Residents said fierce clashes erupted in the northwest districts of Zahraa and Liramun, where tanks fired on rebel positions, and in the embattled Old City.

The Observatory reported army shelling Sunday of the strategic rebel-held town of Maaret al-Numan, the nearby village of Maarshmisha and Idlib city in the northwest province of Idlib.

The army on Saturday retook a stretch of the Damascus-Aleppo highway in Idlib province used to send its reinforcements to main northern battlefields, but has failed to regain control of Maaret al-Numan.

According to Observatory, which relies on a network of activists, lawyers and medics in civilian and military hospitals, fighting also broke out on Sunday south of Ras al-Ain, in Hasakeh province.

The mainly Kurdish province of Hasakeh has seen heavy fighting in the past few days, with 46 combatants killed as the opposition seized Ras al-Ain on Friday.

The Observatory had on Saturday reported that Kurdish residents backed by militia from the Democratic Union Party (PYD) had taken control of three towns near the border with Turkey after convincing pro-government forces to leave.

The PYD has links with Turkey's rebel Kurdistan Workers' Party (PKK).

The watchdog said the residents had feared the same kind of violence that saw 9,000 Syrians flee to Turkey in 24 hours in the face of the fighting in Ras al-Ain.

The Observatory says more than 37,000 people have died since the uprising erupted in March 2011, first as a protest movement and then as an armed rebellion after demonstrations were crushed.