Libyan forces mostly made up of brigades from the western city of Misrata and backed by US air strikes have taken control of one of the last districts in Sirte occupied by Islamic State fighters.
The number of casualties in the battle remains unclear for now.
For three months now, the forces have been involved in a campaign to recapture Sirte helped by US airstrikes .
According to the US Africa command, a total of 48 airstrikes have already been conducted on the terrorists.
Key sites south of central Sirte had been taken last week before fighting reached the zones captured on Tuesday.
The Islamic state took control of Sirte last year extending its control to over 250 kilometres.
Losing Sirte will be a major setback for the Islamic State targeted by US backed campaigns in Iraq and Syria.
Efforts to defeat the terrorist group in Libya have been made difficult by continuous instability as well as the existence of a rival government in the east.