East Libyan forces said they had launched air strikes on Islamic State fighters after the militants made incursions south and east of their former coastal stronghold of Sirte.
IS has grown bolder in recent weeks, setting up temporary checkpoints, attacking local forces, and taking over village mosques to lead prayers during the Muslim holiday of Eid al-Adha, Libyan officials say.
The increased activity has raised concern that Islamic State could regroup around Sirte, from where it was driven out in December by local forces and a US air campaign.
Most militants were killed in the nearly seven-month battle, but an unknown number fled into the desert.
Sirte lies at the centre of Libya’s Mediterranean coastline, on the dividing line between regions controlled by rival Libyan factions.