FIGHTING between rival militias at Tripoli airport has destroyed most of the planes parked there and prompted the UN to evacuate its staff.

In some of the worst violence in months, at least 15 people have been killed in clashes in Tripoli and the eastern city of Benghazi since Sunday, and a Libyan official said several Grad rockets hit the Tripoli International Airport, damaging the control tower.

With its new government struggling to impose order since the 2011 rebellion that ousted Muammar Gaddafi, Libya is sliding deeper into turmoil with rival brigades of former rebels battling for political and economic power.

So far the authorities have attempted to rein in militia fighters by putting them on the government payroll, but months of protests over oilfields and ports have cut into the government's revenues as its economic troubles mount.

A Nato coalition helped rebels topple Gaddafi but the military alliance has not intervened to stem the subsequent chaos despite Libyan hopes it might.