MISRATA, Libya (Reuters) - Libyan forces said they had advanced against some of Islamic State’s last holdouts in Sirte on Saturday as fighting resumed after several days of relative calm.

The forces, which are aligned with Libya’s U.N.-backed government, launched their campaign to recapture the city in May and have been aided by dozens of U.S. air strikes since the beginning of August.

Forces made up mostly of fighters from Misrata, 230 km (145 miles) to the north west, now say they are in the final stages of their campaign to oust Islamic State from its former North African stronghold.

But they have faced stiff resistance from militants holed up in a slowly shrinking residential area in the center of the coastal city, who have defended themselves with car bombs, sniper fire, mines and shelling.

On Saturday the forces said they had captured several buildings between Sirte’s neighborhoods Number One and Number Three, and had destroyed an Islamic State car bomb before it could reach its target, according to updates posted online.

At least seven fighters were killed and 30 wounded, and the bodies of 10 Islamic State militants were found in a school building, they said.

Losing Sirte would be a major blow for Islamic State, which won total control of the city more than a year ago, using it as an important base for Libyan and foreign fighters.