Syrian air raids on two northern towns held by the militant Islamic State group have killed more than 50 people in two days, activists say.

Rami Abdurrahman of the Britain-based Syrian Observatory for Human Rights said today that several air strikes on the towns of al-Bab and neighbouring Qabasin killed at least 53 people, including seven children.

The strikes took place on Thursday. Another Syrian monitoring group also reported the raids, and activists uploaded video of the strikes' aftermaths to social networks.

The Syrian government has been heavily bombing areas held by rebels and the militant Islamic State group in recent days. Rights groups accuse government forces of using bombs that cannot be precisely targeted, causing high civilian casualties.

Video obtained from a social media website purports to show the aftermath of aerial bombardment targeting Islamic State-held areas in the northern city of al Bab, which reportedly killed dozens of civilians.