Government air strikes hit rebel-held areas of Aleppo on Saturday as rockets fired by insurgents pounded neighbourhoods under state control, part of escalating violence in northern Syria that has undermined a truce agreement.

Fatalities were reported on both sides of the city, the focus of a military escalation that has underscored the bleak outlook for UN-led peace talks being convened in Geneva.

The British-based Syrian Observatory for Human Rights, which monitors the five-year-long war, said air strikes had targeted at least four parts of Aleppo. Opposition sources said there had been deaths, but the number was not immediately clear.

The Observatory said three people had been killed in the rebel bombardment of government-held areas of the city. Syrian state news agency Sana put the death toll at seven, saying they had been killed by missile bombardments and sniper fire.

Fighting has intensified this month to the north and south of Aleppo, Syria's biggest city and industrial centre until the country's conflict erupted in 2011.

The fighting has stretched to breaking point a "cessation of hostilities" deal brokered by the United States and Russia with the aim of allowing peace talks to start.-Reuters