Casualties have been reported as armed men stormed on Monday the headquarters of Libyas National Oil Company in Tripoli. Witnesses and a security source said the building near the city center had caught fire and was surrounded by security services. Two NOC staff and two gunmen were killed in the attack, a security official said. "The death toll so far is two killed from NOC staff and two attackers," said Ahmad Ben Salim, spokesman for the Special Deterrence Force (Rada) force, which had surrounded the NOC building. "The situation is under control," he added. He was not able to provide details on the identity of the attackers. The Health Ministry said two people were killed and 10 others were injured in the attack, according to initial information. Health official Malek Merset had earlier said that there were dozens of injuries caused by the gunfire, smoke inhalation or explosions. At least one explosion rocked the building soon after the gunmen went in, starting a fire that swiftly spread through the lower floors, according to the officials. NOC chief in Tripoli Mustafa Sanallah told a Libyan television channel that explosions and an exchange of gunfire between the attackers and the buildings security guards have caused an unspecified number of deaths and injuries. "The building was heavily damaged due to the fire. Smoke is everywhere," Sanallah said. "The gunmen attacked the lower floors with random shooting and explosions. Its a very violent attack." No group has so far claimed the attack. There was no word on the fate of the gunmen, described by Libyan officials as "terrorists," or whether they were still holding hostages. It was not immediately clear either whether the security forces were in control of the building. Earlier, the Interior Minister of the Tripoli-based Government of National Accord, Brig. Gen. Abdul-Salam Ashour, said the attack was carried out by six gunmen and that employees were inside the building when it took place. The UN mission in Libya condemned the attack, describing it as "cowardly" and called on Libya to cease their "futile side conflicts" and unite to rid their nation of terrorism. It comes four months after suicide bombers struck the headquarters of Libyas electoral commission, killing 14 in an attack claimed by the ISIS group. Libyas vital oil sector has been repeatedly disrupted by violence since the 2011 collapse of longtime leader Moammar al-Gaddafi’s regime. Petrochemical exports had accounted for the vast majority of state revenues under his rule, with production at 1.6 million barrels per day. But since his ouster, output fell to about 20 percent of that level, before recovering to more than one million barrels per day by the end of 2017. Oil producers cartel OPEC has estimated Libyas oil reserves at 48 billion barrels, the biggest in Africa.