Libya's interim authorities on Saturday denounced an offensive launched by a rogue general in the restive eastern city of Benghazi against Islamists as a "coup" bid, a statement said.

The offensive by Khalifa Haftar against those he describes as "terrorists" is considered as "an action outside state legitimacy and a coup d'etat," the army, government and parliament said in a joint statement.

Khalifa, a retired general, used air power to pound Islamist positions in Benghazi on Friday, in a campaign to purge Libya's second city of "terrorists" that led to clashes in which 37 people were killed.