America has launched more than 140 air strikes on Islamic State targets in Libya in the past six weeks, as it has stepped up its second front against the militants.
Jets, attack helicopters and drones have hit tanks, trenches, armed pick-up trucks, supply vehicles and fighting positions in the blitz to oust militants from their coastal stronghold of Sirte.
Militia fighters loyal to the UN-backed government have used the air campaign to clear militants from much of the city, but Tripoli suffered a blow to its authority on Monday when a rival force seized the oil port of Zuwaytina.
Two other oil ports were seized by the same militia, commanded by Gen Khalifa Haftar, on Sunday.
Oil is seen as a vital source of income for the Government of National Accord (GNA), which is struggling to assert its authority over the divided country.
US forces have carried out 143 air strikes on Islamic State targets in Sirte at the request of the Libyan Government of National Accord, according to Pentagon figures.
Swathes of the Libyan coast around Sirte were seized by militants loyal to Islamic State in Iraq and Levant (Isil), last year. Western officials were concerned the enclave in the chaotic north African country could become a bolthole for Isil extremists dislodged from Iraq and Syria.
US Marine Corps Harrier jump jets, and Cobra helicopter gunships launched from the amphibious warfare ship USS Wasp, have led the air campaign.
Ash Carter, US defence secretary, has said that American military assistance to the GNA would continue after Islamic State was pushed out of Sirte.
The remnants of the militants are expected to regroup elsewhere, perhaps around Bani Walid, in the far south of the country, or in the east around Benghazi.
Britain last year considered joining an Italian-led training mission to bolster the GNA, but the plan was put on hold after military chiefs raised concerns that sending Western troops into the turmoil would only make the situation worse.
Italy announced it would set up a military hospital and deploy 300 doctors, nurses and soldiers near Misrata airport, Reuters reported.
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