Fierce fighting between Syrian government forces and the Islamic State group has killed 64 combatants in Raqqa province over a 24-hour period, a monitoring group said Wednesday.

The clashes come with the army pressing an advance through Raqqa, in northern Syria, towards neighbouring Deir Ezzor, the only remaining province of the war-ravaged country still in the hands of IS militants.

The Syrian Observatory for Human Rights, a British-based monitor, said the fighting had claimed the lives of 38 militants and 26 pro-government combatants since Tuesday morning.