At least 14 pro-government fighters were killed in clashes with the Islamic State group in the jihadists' former Libya bastion of Sirte, a medical source said.
"Fighting today began at 9am (0700 GMT) and the toll to now is 13 dead and 25-30 wounded," hospital official Abdellatif Abdel Ali said on Friday.
One fighter, who was shot, later died after being operated upon. Ali said the majority of those killed were shot in the head by sniper fire.
Forces allied with Libya's UN-backed Government of National Accord (GNA) have cornered IS fighters in Sirte, 450 kilometres (280 miles) east of Tripoli, since launching an offensive on May 12.
After a pause in fighting on Thursday, pro-GNA fighters resumed the battle against IS holdouts in a seaside residential district of Sirte.
At least three US air strikes hit IS positions on Friday, an AFP journalist in the city said.
A pro-government forces commander told AFP that IS snipers were slowing the anti-jihadist advance.
"These gunmen are well trained and equipped. They haven't given in even with air raids and the seige we've imposed on them," Al-Hedi Issa told AFP.
"So we prefer to advance slowly in order to preserve the lives of our fighters."
The fighting has left more than 550 GNA fighters dead and 3,000 wounded. The IS death toll is not known.