CAIRO — At least six people were killed and 25 injured Sunday when rival militias battled for the control of the international airport in Libya's capital. Civil aviation authorities announced the airport will be closed for three days because of security concerns.Gunfire from the battles echoed through Tripoli as fierce fighting raged between Libyan forces and allied militias and a powerful militia from the western city of Zintan that controls the airport, a member of a revolutionary battalion attached to Libya's army chief of staff that took part in the battle said.Those living in the vicinity said troops surrounded the airfield and fired rockets at buildings inside. Thick columns of black smoke rose overhead and could be seen from downtown Tripoli.The health ministry said six people were killed in the fighting and 25 were wounded.Authorities said Saturday that the airport was to have been handed over into government control. The government largely relies on the same militias to police the streets as its security forces remain in disarray.The powerful Zintan militia had taken control of the airport, providing security for the strategic installation, following the fall of longtime dictator Moammar Gadhafi in 2011.The militias, many of them organized to fight against Gadhafi troops, remained a powerful component in the post-war Libya, filling the void left by weak police and security and cooperating with the government to provide order.But rivalries between militias for control and resources were also the cause for fierce fighting among them; and posed a constant challenge to the central government.On Sunday, the country's civil aviation authority said the airport will be shut for three days pending the security situation, advising airlines to land at other airports in Libya.Egypt's national carrier EgyptAir said it canceled two flights Sunday to Tripoli as hundreds of travelers remained inside the airport waiting for it to re-open. Both British Airways and Turkish Airlines also canceled flights Sunday.