Forces loyal to Libya’s UN-backed government said that 10 of its fighters were on Thursday killed in suicide car bombings carried out by Islamic State in the extremist militia’s former stronghold of Sirte.
Twenty pro-government fighters were also injured in the two bombings, the media centre for the forces said.
The casualties were transferred to a field hospital in Sirte. Government forces are currently engaged in a three-month campaign to drive Islamic State from the central city.
The forces meanwhile killed three militants in a "special operation" in Sirte’s residential First Neighbourhood, one of the last areas under Islamic State's control, their media centre reported without giving details.
The government forces, mainly from Libya’s western city of Misrata, said this week they had recaptured Sirte's Second District from Islamic State.
The advance has left the militants surrounded in the coastal city's First and Third districts, with their only apparent escape route by sea.
Last year, Islamic State controlled a 250-kilometre stretch of Libya's central Mediterranean coast before forces aligned to the nascent UN-backed unity government began operations against the al-Qaeda splinter group in May.
Earlier this month, the United States started airstrikes in support of the Libyan forces against Islamic State in Sirte.
The radical group built up its presence in Libya, taking advantage of a conflict between rival governments based in Tripoli and in the east of the country.
Sirte has since been Islamic State's key stronghold outside Syria and Iraq, where the organization has seized vast territory.
Libya has suffered from military and political chaos since the overthrow of long-time dictator Moamer Gaddafi in a 2011 uprising.