Opposition monitoring groups say airstrikes have killed and wounded dozens of people in the northern Syrian city of Raqqa, the Islamic State group's de facto capital.

The Britain-based Syrian Observatory for Human Rights says 19 people were killed and some 60 wounded when the air raids hit several areas in the city, which has been held by the extremists since 2013.

The Local Coordination Committees said the air raids were carried out by Syrian government warplanes, adding that dozens were killed or wounded.

Both groups say Saturday's air raids struck near the national hospital, a former army base and other neighborhoods.

They say most of the casualties were civilians.