The Iraqi army has dropped tens of thousands of leaflets over the ISIL stronghold of Mosul, warning residents of an imminent offensive to reclaim the city from the jihadist group.

In what has been described as the heaviest bombardment in days by Russian planes, at least 50 civilians were killed in Tuesday’s air strikes on rebel-held parts of Aleppo and nearby villages, according to residents and rescue workers.

The Pentagon says US-led coalition aircraft have been scrambled in Syria to protect American special ground forces from attack by government jets.

There has been heavy fighting in Aleppo as Syrian government forces and rebels battle for control of the city.