BENGHAZI, Libya (Reuters) - Forces loyal to Libya’s eastern-based Libyan National Army (LNA) said on Friday that they had moved into strategic oasis towns in the central desert region of Jufra, clashing with rival factions after conducting heavy air strikes in the area overnight.

The LNA is pushing to expand its presence in central and southern Libya, where it has been vying for control with forces linked to the U.N.-backed government in Tripoli and other opponents.

A military escalation puts at risk international efforts to unify political and armed camps based in the east and west of Libya, which have continued to vie for power despite a U.N.-mediated transition plan struck in late 2015.

The clashes on Friday were between local forces loyal to the LNA and the Benghazi Defence Brigades (BDB), a force that includes Islamists and other fighters who fled the LNA’s advances since last year in the eastern city of Benghazi, residents and officials said.

LNA spokesman Ahmed al-Mismari said 12 fighters had died, six on either side. He said the LNA had taken control of the adjoining towns of Waddan, Hun and Sawkna, though it did not control Jufra air base just west of Waddan.

Video footage from the Waddan, which the LNA’s Zawiya Brigade entered earlier in the day, showed vehicles burning by the roadside and several dead bodies lying on the ground.

The advance came after military officials and residents said LNA fighter jets launched heavy air strikes on Thursday night in Jufra.

Over the past week Egypt has also carried out air strikes in Jufra, as well as in the far eastern city of Derna. It said the strikes targeted militants linked to an attack on Coptic Christians in the southern Egyptian province of Minya, though analysts say the strikes appear designed to help LNA commander Khalifa Haftar, a close ally of Egypt.

Mismari said on Friday that two senior Egyptian militants had been found to be operating in Derna, and that satellite phone calls between Minya and Derna had been made before the attack.

Haftar has been slowly gaining ground while rejecting the U.N.-backed government in Tripoli. The LNA has repeatedly says it expects to take control the capital, though many doubt it has the capacity to do so.

Jufra is just over 500 km (300 miles) southwest of Benghazi, and about the same distance southeast of Tripoli. Mismari said the LNA would next move towards Bani Walid, a town northwest of Jufra.

“Once we have control of the military base of Jufra we will move to the west, to Bani Walid, very gradually, because this is a very dangerous area,” Mismari said.

The recent escalation of violence in Libya’s central desert regions came after dozens of fighters loyal to the LNA were killed last month in a raid on Brak Al-Shati air base near Sabha, the region southwest of Jufra.