Tripoli: Libyan forces battling to oust IS from Sirte said they had made major advances on Wednesday, capturing a convention centre previously used as a base by the militant group, as well as the city's university and hospital.
"Our forces have complete control of the whole of the Ouagadougou (convention) complex - they even advanced some distance beyond the complex," said Rida Issa, a spokesman in the forces' media office.
If the gains are confirmed, it would mark the biggest advance the forces have made for weeks. They come 10 days after the United States began air strikes over Sirte, which fighters say have eased their advance on militants encircled in the centre of the city.
The capture of the Ouagadougou complex would also be an important symbolic victory. The large domed building is a landmark in Sirte, the hometown of late leader Muammar Gaddafi, and was used for meetings and religious instruction by Islamic State after they took control of the city last year.
Forces aligned with Libya's UN-backed government launched their campaign for Sirte in May. Their advance slowed as they approached the centre of Sirte, and the forces, led by brigades from the city of Misrata, have suffered heavy casualties from IS landmines and snipers.
Clashes have been sporadic, with heavier fighting interspersed with lulls that last for several days.
Since August 1, US drones and fighter jets have carried out a total of 29 strikes, targeting several IS emplacements on Monday and a gun-mounted pick-up truck on Tuesday, according to statements by US Africa Command.
In Wednesday's clashes, the government-backed forces said they had also advanced to a cluster of unfinished blocks just west of the centre of Sirte known as the "bone buildings, which had been used by IS snipers.
At least three fighters from the government-backed forces were killed and 11 wounded, Issa said, adding that he expected the toll to rise.
Earlier in the day, Libyan forces said they had lost a fighter jet over Sirte. Issa said the cause of the crash and the fate of the crew could not be confirmed, but IS claimed it had shot down the jet, killing a pilot, according to a statement on a website close to the group.
Libyan militants returning from combat in Syria's civil war helped implant IS in Libya in 2014, but IS has struggled to win support or hold territory as most local people regard it as a malign import dependent on foreign fighters.
Meanwhile, Western countries including the United States, France and Britain said in a joint statement on Wednesday they were concerned by mounting tension around the Zueitina oil terminal in Libya.
Washington, Paris, London and the governments of Germany, Spain and Italy urged a return to government control of all oil and gas installations and called on all parties "to abstain from any act of hostility and avoid all actions that could damage or disrupt energy infrastructure".
Zueitina is one of three eastern oil ports blockaded by Libya's Petroleum Facilities Guard (PFG). The PFG has signed a deal to reopen the ports with the UN-backed Government of National Accord (GNA) in Tripoli, but forces loyal to a separate government based in eastern Libya have threatened to block a resumption of exports.
Libya's National Oil Corporation (NOC) said on Sunday that it was concerned by reports of "imminent conflict" in the vicinity of Zueitina between the PFG and the Libyan National Army (LNA), which is loyal to the eastern government.
In a statement released by the French foreign ministry, the six Western powers expressed their support for efforts by the GNA to "find a peaceful solution to the disruptions affecting energy exports in Libya".
"The Government of National Accord must work with the National Oil Corporation to relaunch oil production in order to rebuild Libya's economy."
"Restarting oil exports is crucial for generating revenues needed to provide for the essential needs of the Libyan people, notably electricity, healthcare and infrastructure," the statement by Western countries said.