Sirte's fall would be a huge setback to the jihadists' efforts to expand their self-proclaimed "caliphate" beyond Syria and Iraq where they have also suffered losses.
Forces loyal to Libya's UN-backed unity government made a significant breakthrough Wednesday in their nearly three-month-old offensive to retake Sirte, seizing a conference centre where IS had set up a base.
"The battle for Sirte has reached its final phase, after the successful offensive by our heroes," said spokesman General Mohamad Ghassri.
The advance comes after the United States launched air strikes on IS positions in Sirte on August 1.
The US military said 36 strikes had been carried out against IS since the start of "Operation Odyssey Lightning".
IS took advantage of the chaos that followed the ouster and killing of longtime dictator Moamer Kadhafi in 2011.
Forces allied with the Government of National Accord on Wednesday seized the University of Sirte campus just south of the Ouagadougou conference centre as well as the Ibn Sina Hospital to the north.
On Thursday they removed IS flags from the conference centre and the university, burned them and replaced them with Libyan flags, said their command centre.
It said they had seized a hotel near the city's port and were clearing a complex of luxurious villas used for hosting dignitaries in the Kadhafi era.
Television aired images of soldiers in recaptured areas waving flags and flashing victory signs.
- Fierce resistance -
The pro-GNA forces said 16 of their fighters were killed and dozens wounded Wednesday in Sirte, Kadhafi's hometown just across the Mediterranean from Italy.
It was unclear how many jihadists were killed, but the centre said at least 20 jihadists had died in fighting for the university campus.
Nine pro-GNA fighters were wounded on Thursday and taken to a hospital in Misrata, 190 kilometres (120 miles) to the northwest, the hospital said.
More than 300 pro-government fighters have been killed and 1,800 wounded in the operation, said medical sources Misrata, where the operation's command centre in based.
They have faced determined resistance from the jihadists who have struck back with sniper fire, suicide attacks and car bombings.
Reda Issa, another spokesman for the pro-government forces, said jihadists still controlled residential neighbourhoods in Sirte next to the sea.
"The liberation of Sirte will only be announced when the whole city is recaptured," he added.
Issa said the pilot and co-pilot of a pro-GNA plane which crashed Wednesday while bombing IS positions in Sirte had been killed and their bodies retrieved, without specifying the cause.
IS claimed to have downed the aircraft.
The Washington Post has reported that US commandos are working from a joint operations centre on the outskirts of Sirte, the first time they have directly supported Libyan forces in the anti-IS fight.
- 'No foreign troops' -
Quoting US officials speaking on condition of anonymity, the Post said the US forces were operating alongside British troops, helping to coordinate American air strikes and providing intelligence.
GNA chief Fayez al-Sarraj said in an interview published Wednesday that his government had asked only for "air strikes which must be very precise and limited in time and geographical scope".
"We do not need foreign troops on Libyan soil," Sarraj told Italy's Corriere della Sera.
Italian Prime Minister Matteo Renzi faced criticism at home on Thursday for reportedly sending special forces to Libya to help the anti-IS fight without approval from parliament.
Renzi's centre-left government has refused to confirm or deny reports that dozens of special forces have been deployed to help with de-mining and training pro-GNA forces.
France last month confirmed it had troops in Libya, saying three of the soldiers had been killed while on a mission there.
That prompted a demand from Sarraj for an explanation about the French presence, which the GNA described as a "violation" of the nation's sovereignty.
--------------------------------------------------------------------------------------------------------------------------
Forces loyal to Libya's UN-backed unity government made a significant breakthrough Wednesday in their nearly three-month-old offensive to retake Sirte, seizing a conference centre where IS had set up a base.
"The battle for Sirte has reached its final phase, after the successful offensive by our heroes," said spokesman General Mohamad Ghassri.
The advance comes after the United States launched air strikes on IS positions in Sirte on August 1.
The US military said 36 strikes had been carried out against IS since the start of "Operation Odyssey Lightning".
IS took advantage of the chaos that followed the ouster and killing of longtime dictator Moamer Kadhafi in 2011.
Forces allied with the Government of National Accord on Wednesday seized the University of Sirte campus just south of the Ouagadougou conference centre as well as the Ibn Sina Hospital to the north.
On Thursday they removed IS flags from the conference centre and the university, burned them and replaced them with Libyan flags, said their command centre.
It said they had seized a hotel near the city's port and were clearing a complex of luxurious villas used for hosting dignitaries in the Kadhafi era.
Television aired images of soldiers in recaptured areas waving flags and flashing victory signs.
- Fierce resistance -
The pro-GNA forces said 16 of their fighters were killed and dozens wounded Wednesday in Sirte, Kadhafi's hometown just across the Mediterranean from Italy.
It was unclear how many jihadists were killed, but the centre said at least 20 jihadists had died in fighting for the university campus.
Nine pro-GNA fighters were wounded on Thursday and taken to a hospital in Misrata, 190 kilometres (120 miles) to the northwest, the hospital said.
More than 300 pro-government fighters have been killed and 1,800 wounded in the operation, said medical sources Misrata, where the operation's command centre in based.
They have faced determined resistance from the jihadists who have struck back with sniper fire, suicide attacks and car bombings.
Reda Issa, another spokesman for the pro-government forces, said jihadists still controlled residential neighbourhoods in Sirte next to the sea.
"The liberation of Sirte will only be announced when the whole city is recaptured," he added.
Issa said the pilot and co-pilot of a pro-GNA plane which crashed Wednesday while bombing IS positions in Sirte had been killed and their bodies retrieved, without specifying the cause.
IS claimed to have downed the aircraft.
The Washington Post has reported that US commandos are working from a joint operations centre on the outskirts of Sirte, the first time they have directly supported Libyan forces in the anti-IS fight.
- 'No foreign troops' -
Quoting US officials speaking on condition of anonymity, the Post said the US forces were operating alongside British troops, helping to coordinate American air strikes and providing intelligence.
GNA chief Fayez al-Sarraj said in an interview published Wednesday that his government had asked only for "air strikes which must be very precise and limited in time and geographical scope".
"We do not need foreign troops on Libyan soil," Sarraj told Italy's Corriere della Sera.
Italian Prime Minister Matteo Renzi faced criticism at home on Thursday for reportedly sending special forces to Libya to help the anti-IS fight without approval from parliament.
Renzi's centre-left government has refused to confirm or deny reports that dozens of special forces have been deployed to help with de-mining and training pro-GNA forces.
France last month confirmed it had troops in Libya, saying three of the soldiers had been killed while on a mission there.
That prompted a demand from Sarraj for an explanation about the French presence, which the GNA described as a "violation" of the nation's sovereignty.
--------------------------------------------------------------------------------------------------------------------------