IS fighters still control several areas of the Mediterranean city, whose capture in June last year sparked fears that the extremist group would use it as a springboard for attacks on Europe.
The fall of Sirte would be a huge setback to the jihadists' efforts to expand their self-proclaimed "caliphate" beyond Syria and Iraq where they have also suffered a string of losses.
Forces loyal to Libya's UN-backed unity government made a significant breakthrough yesterday in their nearly three-month-old offensive to retake the city, seizing a conference centre where IS had set up a base.
The rapid advance comes after the United States launched air strikes on IS positions in the city for the first time on August 1.
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The US Africa Command said 36 strikes had been carried out against IS positions since the start of "Operation Odyssey Lightning", including seven on Tuesday.
IS took advantage of the chaos that followed the ouster and killing of longtime dictator Mummar Gaddafi in 2011 to gain a foothold in the oil-rich North African country.
Libyan television broadcast images of flag-waving soldiers in recaptured areas including the Ouagadougou centre, flashing victory signs as they posed for photographs.
The pro-GNA forces said 16 of their fighters were killed and dozens wounded yesterday in the fighting in Sirte, Gaddafi's hometown which lies just across the Mediterranean from Italy.
It was unclear how many IS fighters were killed, but the centre said that at least 20 jihadists had died in fighting for the university campus.
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