Libyan forces loyal to eastern-based commander Khalifa Haftar said on Monday they had entered Sirte and had taken control of large parts of the coastal city.

East Libyan forces said they had launched air strikes on Islamic State fighters after the militants made incursions south and east of their former coastal stronghold of Sirte.

Forces loyal to Libya's unity government on Saturday freed 13 foreigners held by the Islamic State group in its former coastal bastion of Sirte, the forces said.

A Dutch journalist was killed on Sunday while covering a government-backed offensive against the Islamic State group in their Libyan stronghold city of Sirte, a doctor said.

Libyan pro-government forces killed at least 10 Islamic State group jihadists as they attempted to flee their besieged stronghold of Sirte, the country's unity government said Sunday.

Forces loyal to Libya's UN-backed unity government pushed Sunday into the last areas of Sirte held by the Islamic State group in what was the jihadists' coastal stronghold, a spokesman said.

The United States has begun using attack helicopters to target the Islamic State group in the jihadists' Libyan former stronghold of Sirte, a defense official said Tuesday.

Islamic State group jihadists in Libya have carried out nine suicide bombings in one day in a failed bid to hold a central district of Sirte, pro-government forces said Wednesday.

Libyan forces backed by US air strikes said on Tuesday that they had taken control of one of the last districts in central Sirte occupied by Islamic State fighters.

Libyan pro-government forces battled to seize more territory from Islamic State group jihadists in their stronghold Sirte on Wednesday but their offensive was hindered by mines and snipers.

Libyan forces said Tuesday they were advancing inside the jihadist bastion of Sirte, as Washington conducted a second straight day of air strikes on Islamic State group positions in the city.

The US military conducted air strikes in Libya on Monday following a government request to target the Islamic State group's Libyan stronghold of Sirte, the Pentagon announced.