Activists say Syrian airstrikes targeting a stronghold of the Islamic State extremist group have killed at least 13 civilians.

The Britain-based Syrian Observatory for Human Rights says the eight strikes targeted the northeastern city of Raqqa, which is run by the militant group. The Observatory said at least one strike hit a bakery on a busy street, and that the death toll was likely to rise. The Observatory obtains its information from a network of activists on the ground.

The incident was also reported by a Raqqa media collective.

The Syrian government has increased its airstrikes on Raqqa since fighters of the Islamic State swept into neighboring Iraq, seizing northern and western swaths of that country and declaring a proto-state straddling the border.