Forces loyal to Libya's UN-backed unity government stand next to an Islamic State (IS) group flag in Sirte's centre as they advance to recapture the city from the jihadists on June 10, 2016.
Forces aligned with Libya's unity government said they had taken control of the port of Sirte, making further gains in Islamic State's North African stronghold.
Brigades, largely composed of fighters from Misrata, advanced this week to the perimeter of Sirte's city centre after launching a counter attack against the Islamic State last month and driving the militant group back along the coastal road between the two cities.
The brigades are part of an operation supported by Libya's UN-backed Government of National Accord (GNA), which arrived in Tripoli in March and has been gradually working to establish its authority.
Western powers see it as the best bet for trying to unite Libya's political and armed factions against the Islamic State and for restoring some stability in the oil-rich North African country.
A source from the operations room in Misrata said fighters from the front line in the south of Sirte had looped round to the seafront to capture the port, which lies about 5 km (3 miles) east of the city centre.
The brigades have advanced more swiftly than many expected, though their progress has been hampered by suicide bombers, mines and snipers.
Clashes in Sirte on Friday left 11 brigade members dead and 35 wounded, the operations room source said. More than 100 fighters from the GNA-backed brigades have been killed and more than 500 wounded since the campaign to recapture Sirte began in early May.
The Islamic State started expanding into Libya in 2014 as the political turmoil and conflict in the country worsened. It took full control of Sirte last year, but has struggled to retain territory or win support elsewhere in Libya.
As the brigades based in Misrata have advanced on Sirte from the west, a separate force that controls some of Libya's key oil terminals and is also aligned with the GNA has pushed Islamic State back from the east.