Syria ceasefire hanging by thread after new Aleppo bombing

Four air raids hit rebel-held areas of Syria's Aleppo on Sunday, a monitor said, in the first raids on the battered city since a truce took effect.

The Syrian Observatory for Human Rights said several people were wounded but could not immediately give details about casualties or identify who carried out the strikes.

A halt to fighting around Aleppo and the delivery of desperately needed humanitarian aid were key components of the fragile truce, which began on Monday evening.

While the front lines had remained calm, civilians in the besieged eastern quarters had yet to receive promised food assistance.

The estimated 250,000 people in the eastern half of the city have been living under government siege since early September.

Rebel groups - which have yet to formally sign on to the truce - have regularly pledged to break the encirclement.

The head of Fateh al-Sham Front, which changed its name from al-Nusra Front after renouncing its ties to al-Qaeda, said late Saturday that opposition fighters would do all they could to end the encirclement.

Abu Mohamed al-Jolani said "neither we nor rebel groups will allow the siege of Aleppo to continue".

More than 300,000 people have been killed since Syria's conflict erupted in March 2011 with protests calling for the ouster of President Bashar al-Assad.