CAIRO/TUNIS, Aug 21 (Reuters) - Tunisia and Egypt's Cairo airport cancelled most flights to and from Libya on Thursday, officials said, days after the Libyan government said unidentified war planes had attacked positions of armed groups in Tripoli.

A spokesman for Tunisian Aviation Authority gave no explanation for the measures but Libyan news agency LANA and Egyptian officials said Cairo airport authorities had cancelled flights for security reasons.

Flights from Tunis to the eastern Libyan town of Labraq, as well as from the Egyptian Mediterranean port city of Alexandria to Libya were still operating, a Libyan aviation official said. A Tunisian transport official said flights to the eastern town of Tobruk were also still running.

Flights from Tunisia and Egypt to Libya had been operating on an almost daily basis until now.

Libyan renegade General Khalifa Haftar claimed Monday's attack in Tripoli on Islamist-leaning armed factions which have been trying to expel their rivals from the capital in the worst fighting since the ousting of Muammar Gaddafi in 2011.

But some analysts have questioned how outdated jets from the Libyan airforce - which were severely damaged during the 2011 uprising against Gaddafi - managed to stage a night attack flying 1,000 km from the east.

Haftar has used aircraft in Benghazi to attack Islamist brigades but with mixed success. Once a plane hit a university site instead of a militia camp, residents said.

Libyan television news channels speculated that neighbouring countries or other parties may be behind the overnight air strikes. The United States, NATO and Egyptian officials have denied any involvement. (Reporting by Tarek Amara, Ulf Laessing, Feras Bosalum and Ayman al-Warfalli; Editing by Raissa Kasolowsky)