The commander of Libya's self-styled national army in the east has ordered naval bases to confront any vessel entering the country's territorial waters without military permission.
A statement released by the forces of Field Marshal Khalifa Hifter said the command was directed to eastern bases in Benghazi, Ras Lanuf, Tobruk, as well as the capital Tripoli, in the west, after an Italian patrol boat arrived there.
Italy sent the mission to help the coast guard curb the flow of migrants crossing the Mediterranean, upon request by the UN-backed government in Tripoli.
Libya's eastern-based parliament, a rival to Tripoli and allied with Mr Hifter, strongly opposed the move.
Libya descended into chaos following the 2011 civil war that toppled and killed dictator Muammar Gaddafi.
It is now split between rival governments and militias.