A suspected US air strike on a school being used as a shelter by families displaced from the Isil-held Syrian city of Raqqa killed at least 33 people on Tuesday, in the latest high civilian casualty raid by the coalition.

A school being used by some 50 families in Mansoura, 15 miles from the capital of Islamic State of Iraq and the Levant (Isil)’s so-called caliphate, was levelled by airstrikes on Tuesday morning.

The death toll is expected to rise, according to local activists, who said bodies were still being pulled from the rubble and many families were unaccounted for.