Clashes broke out between rival Libyan militias at Tripoli's international airport Monday after angry gunmen drove armed pickup trucks on to the tarmac and surrounded planes, forcing the airport to cancel flights. In a fresh challenge to the interim government's weak authority, members of the Al-Awfea Brigade force occupied the airport to demand the release of their leader whom they said was being held by Tripoli's security forces, officials said. Weeks before a planned election, Libya's new rulers are struggling to assert their control over an array of former fighters who still refuse to lay down their arms after last year's war that ousted Muammar Gaddafi. Several international flights were canceled, and in some cases passengers who had already boarded planes got off and left the airport. Some flights were diverted to Tripoli's military airport Mitiga, airport workers said. “The situation in the airport is very tense and tanks are surrounding the buildings. No one is allowed into the building,” said the security official, who declined to be named. One Italian passenger who was due to fly out and later arrived at a Tripoli hotel described the situation as “chaotic.” “There were about 200 of them who came into the airport, they were armed. We were waiting to board our flight and we could hear noises, people shouting,” he said. Clashes later broke out when militia groups from Tripoli as well as the mountain town of Zintan arrived at the airport to try to get the Al-Awfea Brigade to leave. He said gunfire could be heard and men were entering the airport carrying rocket-propelled grenades. Repeated calls to government officials were left unanswered. The ruling National Transitional Council spokesman, Mohammed Al-Harizy, said Hebshi was taken by unknown armed rebels while traveling between Tarhouna and Tripoli Sunday night. Monday's violence is the latest in a series of violent incidents as the North African country prepares for its first free polls for a national assembly since last year's war. Last month, one person was killed and several were wounded when militiamen protesting outside the prime minister's office started shooting. In November, about 100 Libyans surrounded a Tunisian passenger aircraft at Tripoli's Mitiga airport, delaying its takeoff in an anti-government protest. Dozens of cars then drove out on to the tarmac, blocking the jet, with passengers on board, from moving.