Islamist fighters launched a three-pronged attack Saturday on a key oil region in eastern Libya but were pushed back by pro-government forces, military officials said.
Fighters from Fajr Libya, an anti-government Islamist coalition, staged an assault on the region of Al-Hilal from three sides but the air force repelled them, said Brigadier General Saqr Jarushi.
"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".
Earlier a statement from Fajr Libya said the Islamist coalition had launched a military operation to "liberate oil fields and terminals".
Jarushi said that after the army fended off the attack, clashes broke out between soldiers and Islamist fighters.
A "state of emergency" was declared in the region, added Jarushi, who is part of anti-Islamist forces led by ex-general Khalifa Haftar battling for control of the capital Tripoli and the eastern city of Benghazi.
Ibrahim al-Jadran, who heads a government unit in charge of guarding Libya's oil installations, said troops were still facing "some pockets of resistance".
Libya's economy took a heavy hit after rebels blockaded export terminals in July 2013, forcing a reduction in output and slashing vital oil revenues.
The seizure of four terminals as part of a campaign for restored autonomy for the eastern Cyrenaica region reduced output from 1.5 million barrels per day to just 200,000.
Under a deal with the government, the rebels returned control of two of the terminals in April and the remaining two in July.
Since then, output and exports have soared, despite unrest rocking a country that never regained stability following the 2011 ouster of long-time dictator Moamer Kadhafi.