At least 19 soldiers were killed in clashes with Islamist militia in eastern Libya, where an oil tank also caught fire in separate fighting, a military source said.
The source said the soldiers were killed in attacks launched by the Fajr Libya movement in Sirte, while the oil tank at the port of Al-Sidra was hit by rocket fire in other clashes.
Al-Sidra is located in a region known as the "oil crescent" that has been the scene of recent clashes between government forces and Fajr Libya.
"14 soldiers were killed in a surprise attack on the 136th battalion responsible for monitoring a power plant west of Sirte," said the source.
Four other soldiers from the same battalion were killed in the clashes that followed, the source added.
But a medical source at Ibn Sina hospital in Sirte said only 18 bodies were received from the fighting.
"The armed forces on Thursday repelled an attack in which the Fajr Libya militia tried to seize the Al-Sidra oil terminal," said Ali Al-Hassi, spokesman of the security services protecting the region's energy facilities.
The 136th battalion is affiliated with the military. Most its fighters are from a tribe loyal to former general Khalifa Haftar.
General Haftar's forces have been fighting alongside forces from the internationally recognised government of Prime Minister Abdullah al-Thani against Islamist militants who have seized control of cities including Tripoli.
Elsewhere, a rocket set a storage tank at the eastern Libyan oil of port Es Sider on fire as armed factions allied to competing governments fought for control of the country's biggest export terminal, officials from both sides.
Clashes were also reported from Sirte, a city west of Es Sider, killing up to 19, among them 14 guards at a power plant, residents said.
No more details were available.
Es Sider and its adjacent Ras Lanuf terminal have been closed since a force allied to a rival government in Tripoli moved east trying to take them.
This is part of a struggle between former rebels who helped topple Muammar Gaddafi in 2011 but now fight for power and a share of oil reserves.
Libya has had two governments and parliaments since a group called Libya Dawn seized the capital in August.
Libya expelled a rival faction, installing its own prime minister and forcing the recognised premier, Abdullah al-Thinni, to operate out of the east with the elected House of Representatives.
Mr Thinni accuses Libya Dawn of relying on Islamists.
The Tripoli-based government says Mr Thinni's forces have allied themselves with former Mr Gaddafi officers such as ex-general Khalifa Haftar.
Ali Hassi, spokesman for a security service allied to Thinni's internationally-recognised government, said the rival force tried taking the Es Sider with speedboats, opening fire on an oil tank.
Ismail al-Shukri, spokesman for the rival force, said it had launched a new push to take the ports but denied it had sent boats or shot at any storage tanks.
He blamed the other side,saying aircraft had attacked the tank.
"A tank was hit but the damage is limited," said Hassi,adding that the advance had been stopped with aircraft and ground troops. Clashes were also reported in Ben Jawad west ofEs Sider.
An oil ministry official said the storage tank was still on fire.
Smoke could be seen on pictures posted on social media websites and described as showing the port.
The fighting has reduced Libya's crude output to 352,000 barrels a day, a spokesman for state National Oil Corp said.
Only the Brega, Sarir, Messla and offshore operations were still producing, he said.
Es Sider and Ras Lanuf ports had been processing an estimated 300,000 bpd.
