Rocket fire forced the suspension of all flights into and out of Tripoli's sole functioning airport on Wednesday, only nine days after it reopened following a truce, Libya's embattled UN-recognised government said.

Mitiga airport had reopened after the truce in nine months of fighting for control of the capital between the Government of National Accord and forces loyal to a rival administration based in the east.

Six military-grade Grad rockets targeted the airport in what GNA forces spokesman Mohammed Gnunu branded a "flagrant threat" to the safety of air traffic and a "new violation" of the ceasefire.

He said the rockets were fired by the "militia" of the "war criminal Haftar", referring to the self-proclaimed Libyan Arab Armed Forces of military strongman Khalifa Haftar that have been battling to take the capital.

Airport management said flights would be suspended indefinitely.

A Libyan Airlines flight from Tunis was forced to divert to Libya's third city Misrata, 200 kilometres (125 miles) east of the capital. Despite repeated appeals from UN envoy Ghassan Salame, Mitiga has been the target of several air raids and rocket strikes since Haftar's forces launched their offensive last April. Haftar's forces, which accuse the GNA of using Mitiga for military purposes, say they target "Turkish drones" being launched from the airport to attack their troops in southern Tripoli.