Tripoli - Fighting raged for control of the Islamic State group's Libya stronghold of Sirte after unity government forces battled their way into the centre of the city.
The United States confirmed the advance on Sirte, the hometown of ousted dictator Muammar Gaddhafi that has also been in the sights of forces of a rival authority in eastern Libya.
The loss of Sirte would amount to a huge setback for ISIS, which is also faced with battlefield reverses in Syria and Iraq.
"The armed forces entered Sirte. They are currently in the centre, where clashes continue with Daesh," said Mohamad Ghassri, spokesperson for the forces of the UN-backed Government of National Accord (GNA).
"The operation will not last much longer. I think we'll be able to announce the liberation of Sirte in another two or three days," he said.
Brett McGurk, US President Barack Obama's special envoy to the international coalition fighting ISIS, confirmed the advance.
Tightening the noose on ISIS, air strikes targeted the area around a conference centre where IIS had set up a command post, while the GNA's navy said it was in control of the waters off the eastern city.
Aziz Issa, a hospital spokesperson in Misrata, east of Tripoli, said a total of 115 fighters had been killed and 300 wounded in the anti-ISIS assault since mid-May.
Stepping up the operation, the GNA's navy has taken control of the coast of Sirte as part of the offensive, said Rida Issa, its commander for central Libya.
"Our forces control the entire coast of Sirte. They (ISIS jihadists) will not be able to flee by sea."
Naval forces had supported the offensive, he said, including by "carrying out operations to open the way for ground forces to advance along the coast".
The unity government said on Wednesday that its forces had captured two military barracks from the jihadists near Sirte, which ISIS has held since 2014.
Since launching the offensive against ISIS in mid-May, GNA forces have taken the town of Abu Grein, the power plant of Sirte and three barracks 20km from the city centre.
And on Thursday they announced the capture of the town of Harawa, 70km east of Sirte.
There has been no independent confirmation of the announced GNA advances over the past three weeks because of the absence of journalists on the ground.
Foreign intelligence services estimate ISIS has 5 000 fighters in Libya but its strength inside Sirte and the number of civilians living in the city are unavailable.