Benghazi - Libya's UN-backed government says gunmen have stormed the headquarters of the country's national oil company in the capital Tripoli and taken hostages.Interior Minister Briadier General Abdul-Salam Ashour says the attack by six gunmen took place on Monday while employees were inside the building. He believes there are casualties from an exchange of gunfire between the attackers and the building's security guards."Our forces will go in and rescue the hostages," Ashour said.Monday's attack followed recent fighting in Tripoli between rival armed groups, which left at least 61 people dead. A cease-fire has been in place since last week.Libya slid into chaos after the 2011 uprising that overthrew dictator Muammar Gaddafi and led to his death. It is now governed by rival authorities in Tripoli and the country's east.