Rebel forces in Libya say they have taken control of Sirte following what media reports describe as a rapid advance on the strategic coastal city.
The UN-backed Government of National Accord (GNA) has not yet commented on the January 6 announcement, which comes amid an offensive by the east-based forces loyal to General Khalifa Haftar to capture Tripoli.
The Libyan capital is the seat of the GNA.
Sirte has been controlled by GNA- aligned forces since fighters of the Islamic State extremist group were expelled in 2016.
Libya has been torn by violence since longtime ruler Muammar Gaddafi was deposed and killed in 2011.
The North African country has two rival administrations, the UN-backed one based in Tripoli, and Haftar's one in the eastern city of Tobruk.
Reuters quoted an unidentified resident as saying that convoys of troops belonging to Haftar's self-styled Libyan National Army (LNA) could be seen inside Sirte.
"They control large parts of the city now. We also hear gunfire," the resident said.
The reports come a day after Turkish President Recep Tayyip Erdogan announced he had dispatched military elements to Libya to ensure stability for the GNA, after parliament approved the move last week.
Ankara has given no details about the scale of its military deployment, but Foreign Minister Mevlut Cavusoglu said on January 6 that Turkey would send military experts and technical teams, adding, "How and when this will happen is to be decided by the government, under the president's leadership."
The UN-backed government is supported by NATO-member Turkey and its ally Qatar.
Haftar is backed by the United Arab Emirates, and others, including what is believed to be a force of Russian private military contractors.
Also on January 6, the UN's Libya envoy said that a country supporting Haftar's forces was likely responsible for a deadly drone attack on a military academy in Tripoli.
Speaking after briefing the UN Security Council, Ghassan Salame called on foreign powers to "keep out of Libya."
At least 30 people were killed in the January 4 air strike.
Libyan Rebels Say They Seized Key Coastal City