Syria's state media say rebels have fired mortar shells at the central prison in an embattled northern city, killing and wounding several inmates.

The pro-opposition Aleppo Media Center says clashes are underway between rebels and government troops at the prison in Aleppo. The center says a large fire has broken out at the facility.

Friday's fighting comes a week after President Bashar Assad's forces repelled a rebel raid on the prison that sought to free hundreds of political prisoners.

The Britain-based Syrian Observatory for Human Rights says intense fighting is also going on in the town of Qusair, near the border with Lebanon.

Government forces have been trying to recapture the town since Sunday. State-run news agency SANA says troops killed a "large number" of rebels in the latest clashes.