Forces aligned with Libya's UN-backed government, supported since Aug. 1 by US air strikes, have pushed militants back into a small residential area in central Sirte in a three-month-old campaign. Heavy fighting resumed on Sunday after a one-week lull.
The Libyan brigades, mostly from the city of Misrata, say they are close to victory in Sirte, but they have struggled to defend themselves against suicide bombings, sniper fire and landmines.
On Sunday, several brigades stationed close to Sirte's seafront advanced several hundred meters eastwards through Sirte's neighborhood Number One, while other fighters overran ISIS positions in street-to-street fighting to the south.
Fighters used tanks, rocket-propelled grenades and anti-aircraft guns to try to blast through ISIS sniper positions.
The Misrata-led brigades said there had been five attempted car bombings on Sunday in a "desperate attempt to disrupt the advance", though at least one of the bombs had been destroyed before it could reach its target.
The front lines in Sirte were quieter earlier this week as government-led forces said they were giving time to the wives and children of ISIS fighters to leave the battle zone.
Almost all the city's estimated 80,000 residents left after ISIS took full control of the city last year, turning it into its regional stronghold and expanding its presence along about 250 km of coastline.
The United States has carried out dozens of air strikes against ISIS positions and vehicles in Sirte. This week the US Africa Command said Marine AH-1W SuperCobra helicopters were being used in the operation, alongside jets and drones.
Libyan commanders say some ISIS militants probably escaped around the start of the campaign to recapture Sirte in May, and their forces have been trying to secure the desert to the south and west of Sirte.