Libyan officials and witnesses say the country's Islamic State affiliate has attacked a rival Islamist group in the central city of Sirte and is shelling a residential area.

There were no reports of casualties in Thursday's fighting. But clashes since Monday have killed 46 people.

Local journalist Ezzeldin Ahmed says a group of ultraconservative Muslim clerics had refused to pledge allegiance to IS and urged residents in the northern part of the city to rise up against it. He says one of the clerics was found dead Monday, setting off the clashes.

Libya has slid into chaos since the 2011 overthrow and killing of longtime dictator Moammar Gadhafi. It is now divided between an elected parliament and government in the east, and an Islamist militia-backed government based in Tripoli.