BENGHAZI, Libya (Reuters) - East Libyan forces said on Wednesday they had carried out air strikes and a ground attack on an air base controlled by rivals from the western city of Misrata, prompting a pledge of retaliation from the government in Tripoli.

Tamanhent air base, near the city of Sabha, is on a frontline between loose armed alliances based in eastern and western Libya that have been vying for power in an on-off conflict since 2014.

The eastern-based Libyan National Army (LNA) has been gaining ground in recent months and had committed to pursuing opponents in the desert region north and east of Sabha after losing and recapturing two key oil ports last month.

“The General Command announced today the launch of military ground operations to liberate Tamanhent base ... with the participation of the air force,” said LNA spokesman Ahmed al-Mismari.

The leadership of a U.N.-backed Government of National Accord (GNA) in the capital, Tripoli, condemned the move and said it had ordered its forces to help repel the attack.

“We strongly warn against this continuing and unjustified escalation and tampering with the security and stability of the homeland, which opens the door to a civil war,” it said in a statement.

The GNA is largely aligned with Misrata, the most militarily powerful city in western Libya. But it has failed to win endorsement from factions in the east, who are aligned with LNA commander Khalifa Haftar.

Haftar has repeatedly stated his intention to “liberate” Tripoli, though many believe he lacks the means to take the capital.

Mismari said ground clashes at Tamanhent, which were confirmed by a resident, were continuing late on Wednesday. It was not immediately clear what damage or casualties had resulted from the fighting.

Also on Wednesday, a group of 16 LNA troops wounded in earlier fighting were flown to Italy for medical treatment. Italy evacuated a first group last month.