Fierce clashes between Libyan forces and the Islamic State of Iraq and Levant in Sirte, ISIL's only stronghold in the country, have left at least 36 dead and almost 150 wounded.
Tuesday's fighting resulted in one of the heaviest tolls in the month-long campaign by the pro-government coalition of armed groups that is trying to retake the city from ISIL fighters.
ISIL had been fighting hard to defend the shrinking territory it still controls in the residential centre of Sirte, said Abdalla Binrasali, a spokesman at the forces' media centre in Misrata.
"The resistance was fierce and they were firing with everything they've got, mortars, rockets and rifles," he said. "They fear that if they lose more ground they will be defeated."
Brigades largely composed of fighters from Misrata launched an offensive to take back Sirte from ISIL last month.
They rapidly recaptured ground west of Sirte at the end of May, but their advance slowed as they closed in on the centre of the coastal city.
On Tuesday, fighting escalated and the brigades said they had taken control of parts of the "700" neighbourhood, the broadcasting and electricity company headquarters and a mosque.
The "700" neighbourhood is strategically important because ISIL snipers have been positioning themselves on the district's taller buildings.
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The brigades based in Misrata are aligned with a UN-backed unity government that arrived in Tripoli in March.
It is seeking to replace two other rival governments that were set up in Tripoli and the east in 2014, and to unite Libya's many political and armed factions.
ISIL took advantage of Libya's political turmoil to establish a presence in several of the country's towns and cities from 2014.
It took full control of Sirte, the hometown of the late Libyan leader Muammar Gaddafi, last year, creating its most significant base outside Syria and Iraq. However, the armed group has struggled to retain territory elsewhere in Libya.
Meanwhile, the state LANA news agency said an explosion at a depot on Tuesday in the town of Garabuli, near Tripoli, followed clashes with militias and killed 29 civilians.
According to a statement on the Facebook page of the Qarabouli municipal council, the clashes took place between militiamen in charge of the town security and armed local protesters. When the protesters stormed the militia's barracks, the depot exploded, the statement said. It said that the depot housed firecrackers, not ammunition.