ISIS claimed responsibility for a gun attack on the headquarters of Libyan state oil firm NOC in Tripoli, the militant group's news agency said on Tuesday.
The assault on Monday killed two NOC staff and wounded 10, said officials, who described the three gunmen — who were also killed — as "Africans".
The attack targeted the "economic interests of oppressing governments funding crusaders," a statement carried on the militants' Amaq news agency said.
It was the first assault of its kind against the leadership of Libya's state oil industry.
On Monday, the three men attacked the headquarters of the National Oil Corporation before blowing themselves up.
A powerful brigade operating under the interior ministry, known as the Special Deterrence Force, or Rada, released photos of the attackers as they rampaged through the NOC carrying guns, grenades and explosive belts.
CCTV showed the attackers walking in at 8.51am and shooting at people. It’s unclear exactly when the suicide belts were detonated but at least two attackers were still standing at 9.07am.
Rada also shared graphic photos of the men after they detonated their suicide vests.
Rada, a religiously conservative group that bills itself as an anti-terror outfit, is just one of many brigades that have been integrated into government security forces but who operate as they please.
Despite the criticism levelled at groups like Rada, they secured the scene when the NOC was attacked and took oil chief Mustafa Sanallah to safety.
The state oil company has been praised as one of the few truly functioning Libyan institutions in a country wracked by turmoil and corruption. Production is currently hovering at about one million barrels per day.
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“Far more important than the considerable damage to our building is the human cost of such an attack. Our people are our most precious asset. NOC will not change in its mission because of such actions – we will stay strong and resolute,” said Mr Sanallah.
“There has been no impact on production and operations. This incident, however, serves to demonstrate the fragile security situation in our country and the need for additional measures to ensure NOC is able to withstand those that seek to halt Libya’s recovery,” he said.