Benghazi/Algiers: Firefighters have put out fires started by an attack by IS militants at the major Libyan oil terminal of Ras Lanuf, a spokesman for guards at the terminal said on Sunday.
At least five of the terminal's 13 tanks were damaged as a result of Thursday's attack, firefighters have said.
One of the tanks collapsed completely.
Petroleum Facilities Guard spokesman Ali Al Hassi said authorities were still assessing the extent of the damage.
The National Oil Corporation (NOC) has said it fears that up to 3 million barrels of oil could be lost and that the terminal, shut since December 2014, faces a lengthy closure.
Libya has been riven by violence and political turmoil following the uprising that overthrew Muammar Gaddafi in 2011.
Rival governments backed by armed factions in Tripoli and the east have battled for power and a share of the country's oil wealth.
The IS militants drove into the oil storage site and clashed with security guards before retreating and firing from a distance to set tanks on fire, NOC spokesman Mohamed Al Harari said on Thursday.
IS militants have taken advantage of a security vacuum to establish themselves in the city of Sirte, about 200 km (125 miles) along the coast to the west of Ras Lanuf and the nearby terminal of Es Sider, which is also closed.
On Saturday, armed forces allied to Libya's eastern government said they had carried out airstrikes on Ben Jawad, a town where IS militants have recently consolidated their presence.
It lies just 30 km (19 miles) west of Es Sider on the road to Sirte.
Libya's oil production has dropped to under 400,000 barrels per day, less than a quarter of a 2011 high of 1.6 million bpd.
Meanwhile, Algerian authorities have detained over 200 Moroccans at Algiers airport and summoned the Moroccan envoy to explain an "unusual" increase in the number of Moroccans apparently trying to cross into Libya, airport and government officials said on Sunday.
The foreign ministry and sources at the airport did not confirm why the Moroccans had been held.
"The question about the massive and unusual flow of Moroccans from Casablanca heading for Libya through Algeria in the last weeks was the reason for discussions with the ambassador," Algeria's foreign ministry said in a statement published on APS state news agency.
The current "particularly delicate" security situation required more vigilance and cooperation, the statement said without giving details.
The ministry did not mention the detentions.
But a security source at Algiers airport said 270 Moroccans had been arrested on Saturday night.
The source said the Moroccans were considered suspect because they did not have legal residence in Libya, though it was unclear if they had ties to militant groups.
Moroccan officials were not immediately available to comment on the detentions.