Libyan brigades aligned with a new U.N.-backed government in Tripoli lost 10 men and had another 40 wounded in fighting close to the Islamic State stronghold of Sirte on Wednesday, a hospital spokesman said.
The brigades, mostly composed of fighters from the western city of Misrata, have advanced to the outskirts of Sirte over the past week and say they intend to recapture the city.
On Wednesday they had gained ground south of the city, and at a power station west of Sirte, according to statements posted on their social media accounts. They said they had faced four suicide car bombings, two of which had exploded before reaching their targets.
The extremist group established a foothold in Libya amid political chaos and conflict in the North African state, gaining control over Sirte last year.
Earlier this week a separate force that guards key oil terminals east of Sirte also advanced towards the city, taking control of two small towns previously controlled by Islamic State.
In Sirte itself, a resident told Reuters that a senior cleric had toured the streets on Tuesday urging people to stay in the city and fight.
Most of Sirte's population of about 80,000 is thought to have fled, and the government-backed brigades have said they want to give those residents who remain a chance to escape before advancing into residential areas.
The brigades had already seen 75 of their fighters killed and more than 350 wounded before the latest casualties.