TRIPOLI, June 18 (Xinhua) --- Libya's state-owned National Oil Corporation (NOC) confirmed on Monday that the militant attack on the oil ports caused a decrease of 400,000 barrels in storage capacity.

"The NOC confirms the loss of storage tanks 2 and 12 at the Ras Lanuf port terminal following Thursday's armed assault by the militia in the oil crescent, led by Ibrahim Jathran," the corporation said in a statement.

Jathran is a wanted former chief of the oil installation guards service.

"This has resulted in a 400,000 barrel reduction of crude oil storage capacity (from 950,000 barrels to 550,000 barrels). Prior to the attack, Ras Lanuf had five crude oil storage tanks. The destruction of tank 2 risks leaking and spreading the blaze to reservoirs 1, 6 and 3," the statement explained.

The corporation also demanded "immediate withdrawal of Jathran and his gangs from the port, cessation of military operations, and support and assistance to fire-fighting teams trying to reach the tanks ablaze."

"This incident will result in the loss of hundreds of millions of U.S. dollars in construction costs, and billions in sales loss. Rebuilding the tanks may take years, especially under current security circumstances," it warned.

Benghazi Defense Brigades, a militant group allied with Jathran, launched an attack on the Libyan oil crescent region and clashed with the army forces there on Thursday.

NOC evacuated all employees from the area. It was estimated that the attack caused losses of 240,000 barrels of oil in daily production.

The oil crescent region is located some 500 km east of the capital Tripoli. It contains the country's largest oil ports.

The UN Support Mission in Libya condemned the attack, warning that "this dangerous escalation puts Libya's economy in jeopardy and risks igniting a widespread confrontation."