There was heavy fighting between opposition rebels and pro-government forces in Aleppo's western and southern districts overnight, while the opposition-held Idlib province to the west came under heavy bombardment.

The Britain-based Syrian Observatory for Human Rights said at least 22 people were killed in 26 airstrikes across Idlib on Sunday. The monitoring group also reported later in the day that at least 15 opposition rebels were killed in a suicide bomb attack on a bus carrying fighters across the border from Turkey into Idlib. The province is a major stronghold for the rebel alliance battling forces loyal to President Bashar al-Assad. It also serves as an important base for opposition campaigns in Aleppo, Syria's second largest city.

The Observatory said 45 civilians were killed in raids on Aleppo, which came as one of the rebel factions fighting for control of the city announced it had begun a new offensive "to liberate" the government-held western Zahraa neighborhood.

Divided city

Aleppo, once Syria's financial hub, has become the focal point of fighting between Syrian government forces backed by Russia in the west and opposition rebels in the east. At the same time, the city is still home to some 2 million people, most of whom live in the government-controlled districts.

Observatory head Rami Abdurrahman said the government air raids on Aleppo had intensified since the end of July, when rebels launched an offensive to break a three-week siege of opposition-held neighborhoods. The Observatory said Sunday that the strikes had killed 122 civilians in the past fortnight, while 327 people have died in fighting and shelling.

The escalation has been met with global concern, with the UN and international leaders calling for regular 48-hour pauses in fighting to allow humanitarian aid to reach civilians living in the city.

Elsewhere in Syria, the Local Coordination Committees, an activist network, said Russian jets had struck the Idlib towns of Jisr al-Shaghour and Binnish. Meanwhile further east, Kurdish-led forces backed by the United States were seeking to extend their gains after recapturing the strategic town of Manbij from "Islamic State" militants.

More than 280,000 people have been killed in the war in Syria, which began in 2011 as an uprising against the government of President Assad.

nm/jm (AFP, Reuters, AP)