The Libyan capital's only operational airport has closed again after threats by forces loyal to renegade military commander Khalifa Haftar, dealing another setback to peace efforts.Despite repeated appeals from the United Nations, the airport has been hit multiple times since the start of an offensive in April by fighters led by eastern-based commander Haftar to seize Tripoli from the UN-recognised Government of National Accord (GNA).Mitiga airport authorities said late on Wednesday they were suspending air traffic "until further notice" after Haftar's spokesman threatened to attack planes flying over the city.Mesmari said the internationally-backed government was using the airport for military purposes as a base for Turkish soldiers sent by Ankara to support the GNA. Turkey has backed the GNA, deploying troops to Libya since early January under a controversial November deal with the Tripoli-based administration. Ankara also signed a maritime agreement with the GNA which saw Turkey claim extensive areas of the Mediterranean sea to be explored.Earlier on Wednesday, the airport had suspended flights for several hours after it was targeted by six rockets in an offensive the GNA blamed on its rivals in Libya's five-year civil war, and called a "flagrant threat" to the safety of air traffic. The attack took place just nine days after the facility reopened following a truce.BIG READ | Turkey says Haftar 'only problem' in way of Libya peaceHaftar's offensive on the capital has threatened to plunge Libya into chaos rivalling the 2011 conflict that led to the removal and killing of longtime leader Muammar Gaddafi.International effortsWorld powers have stepped up efforts in recent weeks to find a political solution to the grinding conflict, with neighbouring Algeria the latest country to host a meeting on it set for Thursday.The Algerian foreign ministry said chief diplomats from Tunisia, Egypt, Sudan, Chad, Niger and Mali would meet in Algiers to advance "a political settlement to the crisis through an inclusive dialogue between all parties". ALSO READ | Turkey threatens to 'teach lesson' to Libya's Haftar after peace deal snubAlgeria, which has stayed neutral in the Libyan conflict, shares a border of almost 1 000km with its neighbour.On Sunday, world powers with interests in the conflict convened at a peace summit in Berlin, where they pledged to halt foreign interference, honour a widely violated arms embargo, and support a UN-facilitated political process.