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.
“Fourteen 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.
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.