Nearly three months into a campaign to recapture the city, brigades mainly composed of fighters from nearby Misrata are waging sporadic street battles in residential areas where militants use snipers, mines and concealed explosives to defend their positions.
The brigades advanced rapidly on Sirte after launching a counter-attack against Islamic State (ISIS , ISIL, IS and Daesh) in early May, but their progress has slowed as they close in on the city centre.
Losing Sirte would be a major blow for Islamic State, which established total control over the coastal city last year and expanded its presence along about 250 km (150 miles) of sparsely populated land on either side.
The brigades fighting Islamic State are aligned with Libya's UN backed government, which arrived in the capital, Tripoli, in March.
Friday's fighting was focused on the "Dollar neighbourhood", about 1.5 km southwest of the middle of the city.
"Despite the obstacles and difficulties we have faced in the Dollar neighbourhood such as land mines, booby traps and snipers, the snipers took all the roofs of the high buildings, despite that we made a good progress forwards and we hope to liberate the whole of Dollar neighbourhood and advance further to neighbourhoods number 1, 2 and 3 which means the end of the war, God willing," said fighter, Mohamed.
At least five brigade members were killed and 28 wounded in the fighting, medical officials at a nearby field hospital said.
Nearly all Sirte's residents have left the city, and shots and artillery fire ring out amid emptied buildings now used by both sides for cover.
Islamic State still holds several strategic sites in central Sirte, including the university, the main hospital, and the Ouagadougou conference hall, where fighters believe they have stocked large quantities of ammunition and provisions.
More than 300 of the fighters have died and more than 1,500 have been wounded since the campaign began. After heavy fighting, the brigades tend to hold back for several days, partly because of a lack of capacity to treat the wounded.
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