Libyan forces faced fierce resistance on Saturday from Islamic State militants defending a final strip of land in their former stronghold of Sirte, losing at least five men, officials said.

Forces led by fighters from the city of Misrata and backed by US air strikes have taken all but a few dozen houses near Sirte's Mediterranean seafront since they began their campaign to recapture the city in May.

As the battle has worn on they have advanced more cautiously, trying to limit casualties among their fighters and among civilians and captives trapped with the militants.

Islamic State militants have defended their positions using snipers, tunnels, and hidden explosives.

The Misrata-led forces said in statements posted on social media accounts that they faced two suicide bombers, one using a belt and the other grenades. They also said that "a woman from Daesh (Islamic State) betrayed our forces and fired towards them when they try to provide a safe passage for her".

A Reuters reporter saw Libyan forces suffering casualties as they tried to advance after using tanks and heavy machine guns being used to destroy Islamic State-held buildings.

Five fighters from the Libyan forces had been killed and 18 wounded in the clashes said Akram Gliwan, a hospital spokesman in Misrata.

The Misrata-led brigades said they had nevertheless managed to take control of new houses in the contested Ghiza Bahriya district.

Islamic State took full control of Sirte early last year, extending its presence along about 250km (155 miles) of Libya's coastline.

Sirte's loss would leave the militant group without any territory in the North African country, though some of its fighters escaped during the early stages of the campaign and officials fear they will wage an insurgency from the south and west of the city.

The US has carried out at least 420 air strikes since beginning an air campaign against Islamic State in Sirte on August 1.