Turkey said Sunday that six of its nationals were being held by a Libyan force and vowed to respond to any attacks on its vessels or interests.
The Turkish Foreign Ministry said in a statement it would consider Field Marshal Khalifa Haftar's "illegal militia forces" to be "legitimate targets" if the Turks are not released.
Earlier, Turkish Defense Minister Hulusi Akar said there would be "heavy" consequences to any "hostile attitude or attacks."
His comments came after a spokesman for Haftar's self-styled Libyan National Army called Turkish assets in Libya "legitimate targets," accusing Turkey of helping rival militias allied with the U.N.-supported government. Haftar's forces have received aid from Egypt, the United Arab Emirates, Russia and France.
Akar said Turkey was in Libya to support "regional peace and stability." His comments were carried by the official Anadolu news agency.
The LNA controls much of eastern and southern Libya. In April it launched an offensive against Tripoli, where a weak, U.N.-aligned government is based.
Authorities in areas under Haftar's control asked Turkish nationals to leave the country.
Libya's parliament, which is based in the east and allied with Haftar's forces, barred all ministries, state institutions and banks from dealing with Turkish companies and ordered a ban on Turkish exports.
Restaurants in the eastern city of Benghazi have started to change out Turkish names to avoid reprisal. A popular restaurant in the city, where Haftar's forces are based, announced that it would change its name "in solidarity with our beloved country," referring to Libya.