Libya's eastern Es Sider oil export port has stopped working due to clashes nearby, according to an oil official.
The Ras Lanuf port, east of Es Sider, is still working, the official told Reuters news agency on Sunday, but al-Waha Oil Company which runs the Es Sider port had halted work.
Armed groups on Saturday launched an attack against al-Hilal, a key oil region in the country.
Fighters from Fajr Libya, an anti-government coalition, attacked al-Hilal from three sides on Saturday but the air force repelled them, Brigadier-General Saqr Jarushi said.
"Air force jets and helicopters struck the fighters as they advanced on Al-Sidra oil terminal," he said, adding that the air raids had caused "a large number of casualties".
There was also fighting on the ground in which five government soldiers were reported wounded.
Earlier Fajr Libya said it had launched an operation to "liberate oilfields and terminals" and that two of its fighters were killed and several wounded.
Al-Hilal is the location not only of Al-Sidra but also of the Ras Lanuf and Brega terminals.
The attack comes as rebel forces in the eastern town of Derna say they have formed a new coalition before an expected assault by pro-government forces.
More than three years after a NATO-backed uprising toppled and killed Muammar Gaddafi, Libya remains awash with weapons and powerful militias, and has rival governments and parliaments.
Self-declared Islamist groups have seized Tripoli and second city Benghazi in the east, and forces loyal to Abdullah al-Thinni, Libya's internationally recognised prime minister, are fighting to regain control of them.
Source: Al Jazeera and agencies