Libya's National Oil Corp. issued a "cry for help" as Islamic State militants attacked a second oil tank in the region of Es Sider, the country's biggest oil port which has been closed for more than a year.

Two members of the Petroleum Facilities Guard were killed and 16 others wounded in clashes with Islamic State militants west of Es Sider oil port, guards spokesman Ali al-Hasy said by phone. The militants attacked an oil tank in Es Sider, setting it on fire, according to a statement on the NOC website. Islamic State had shelled a tank in the nearby Ras Lanuf oil terminal region on Monday during a clash with the guards.

"We are helpless and not being able to do anything against this deliberate destruction to the oil installations" in Es Sider and the nearby Ras Lanuf oil terminals, NOC said. "National Oil Corporation urges all faithful and honorable people of this homeland to hurry to rescue what is left from our resources before it is too late."

Islamic State militants previously tried to attack Es Sider in October, killing one guard, but were repelled at the gate of the terminal by the petroleum guards. Es Sider and Ras Lanuf terminals have been closed to oil exports since force majeure was declared in December 2014 when armed groups attacked the ports. Force majeure is a legal status protecting a party from liability if it can't fulfill a contract for reasons beyond its control.