East Libyan forces resumed air strikes against rival factions on Sunday as they tried to push them back from positions around the major oil terminals of Es Sider and Ras Lanuf, a military spokesman said.
The eastern-based Libyan National Army (LNA) is attempting to regain control of the ports after being forced to withdraw on Friday by an attack by the Benghazi Defence Brigades (BDB).
On Sunday afternoon, LNA warplanes targeted positions near Es Sider and south of the coastal town of Ben Jawad, about 30 km (20 miles) to the east, LNA spokesman Ahmed al-Mismari told Reuters.
There were also clashes between the rival forces on the ground, security and oil officials said, though it was not immediately clear whether either side had advanced.
The ports are among Libya's largest, though both terminals were badly damaged by previous rounds of fighting and have been operating far below their pre-conflict capacity.
The fighting, which is linked to a broader, stop-start conflict between political and military factions based in eastern and western Libya, threatens efforts to revive Libya's oil production.
National output more than doubled after the LNA took control of the oil ports of Es Sider, Ras Lanuf, Zueitina and Brega in September. All the ports except for Brega had long been blockaded.
Production has recently been fluctuating around 700,000 barrels per day (bpd), but remains far below the 1.6 million bpd Libya was pumping before the 2011 uprising that ousted its veteran ruler Muammar Gaddafi. Since then, the North African country has been riven by chaos and factional fighting.
The BDB are partly made up of fighters who fled Benghazi as the LNA advanced. The LNA has been waging a military campaign for nearly three years against Islamists and other opponents in the eastern city.