BENGHAZI, Libya- An oil storage tank at the Ras Lanuf port in Libya was ignited amid continued fighting on Sunday, a firefighting official said.

Ras Lanuf's storage tank No. 2 held 200,000 barrels of crude at the time, the official said. Another Ras Lanuf tank, No. 12, had already been set alight and damaged on Thursday, when armed groups stormed Ras Lanuf and the neighbouring terminal of Es Sider.

Groups opposed to Khalifa Haftar's Libyan National Army (LNA), which has held ports in the oil crescent since 2016, mounted Thursday's attack. It led the National Oil Corporation to shut the terminals and evacuate them, declaring force majeure on exports.

The NOC said the immediate production loss was 240,000 barrels per day, which was expected to rise to 400,000 bpd if the ports stayed shut.

The fire fighting official said tank No. 2 might have been hit by a projectile or been set alight when the fire from tank No. 12 spread.

Tank No. 12 held 240,000 barrels of oil and firefighting crews were running out of foam to extinguish the fires, he said.

LNA sources have said they are preparing a counter-offensive, and there have been daily air strikes in the area since Thursday.

The NOC called on Saturday for Ibrahim Jathran, the leader of an armed group who announced Thursday's attack, to immediately withdraw from the ports, warning of further damage to key infrastructure.

Jathran had previously controlled and blocked the ports, before losing them to the LNA.

(Reporting by Ayman al-Warfalli, writing by Aidan Lewis and Ulf Laessing; editing by Jason Neely, Larry King ) ((Ulf.Laessing@thomsonreuters.com))