At least eight members of Libyan pro-government forces were killed Saturday during a fresh offensive on Islamic State (IS) group holdouts in the Islamist militants' stronghold of Sirte, a medical source said.

Forces supporting the Government of National Accord (GNA) -- Libya's UN-backed, Tripoli-based administration -- launched a bid to retake the city from IS six months ago.

They quickly seized large chunks of the city, but the offensive slowed amid an effort to avoid losses and to protect civilians still trapped by the Islamist militants.

A hospital where pro-GNA forces are treated said on Saturday that it had received eight dead and 17 wounded fighters.

The loyalist forces' press centre said on its Facebook page that IS had carried out two suicide attacks. It added that a woman had opened fire as troops tried to secure an escape for her from a house retaken from the militants.

Pro-GNA fighters said they had taken around 30 buildings from IS in Sirte, the former hometown of longtime dictator Moamer Kadhafi, which is around 450 kilometres (280 miles) east of Tripoli.

Six months of fighting have left nearly 700 GNA fighters dead and 3,000 wounded. The death toll for the Islamist militants is not known.