Libya's pro-government forces say suicide bombers detonated two cars near their forces in the Islamic State group's former stronghold city of Sirte, killing at least eight.

Ahmed Hadia, a spokesman for troops loyal to the U.N.-backed government who are fighting to liberate the city, says the attack came in the western part of Sirte on Thursday, and that he expects the death toll to rise since many troops are badly wounded.

Hadia says he believes IS fighters from outside the city staged the attack. Sirte is IS's final bastion in the country, and Libyan troops have been forcing the militants into ever-smaller bits of territory there, backed by the U.S. airstrikes.

Washington says the bombing campaign is critical, with the goat to deny IS a safe haven in Libya.