Sanalla said there were still militants present in the area of the terminals, which were closed on Thursday following an early morning attack by opponents of eastern-based Libyan commander Khalifa Haftar.

One crude oil storage tank in Ras Lanuf was hit and ignited on the first day of fighting, and a second tank caught fire on Sunday.

“We look to fight the fire first of all, stabilize the situation,” NOC Chairman Mustafa Sanalla told reporters in Vienna ahead of a meeting of OPEC and non-OPEC producers on June 22-23.

“Our staff are working very hard in very difficult conditions. The criminals did not give our staff the permission to fight the fires properly until now.”

One Libyan oil source put the output loss as high as 425,000 bpd.

The NOC says the fires have caused “catastrophic damage”, slashing storage capacity at Ras Lanuf by some 400,000 barrels.

On Tuesday a firefighter said that Ras Lanuf’s tank No. 12, which had caught on fire on Thursday, had collapsed.

The NOC has also warned of the risk of fire spreading to tanks Nos. 1, 3 and 6 from tank No. 2, which caught fire on Sunday. Three out of the four tanks at Ras Lanuf that were still working normally.

More than half the tanks at Ras Lanuf and Es Sider, which together are Libya’s largest export terminals with a potential joint capacity of 600,000 bpd, had been damaged or destroyed in previous rounds of fighting.

Before the latest output drop, OPEC member Libya had been producing just more than 1 million bpd of oil.

Libya was exempted from more than a year and a half of coordinated output cuts by OPEC and non-OPEC producers as its oil production partially recovered from years of disruption caused by blockades, conflict and political disputes.