(CNN) -

Control of Tripoli International Airport changed hands Saturday evening after an alliance of Islamist militias from around Libya seized the reins from a rival group.

Fighting was intense and spread from around the airport to other parts of Tripoli. Fighter jets from an unknown source struck locations used by the alliance -- known as the Libya Dawn forces -- killing at least 12 Misrata militiamen, according to the Libyan state news agency, LANA.

Air traffic has been interrupted since the fighting began, with most international carriers suspending flights in and out of Libya.

The airport had previously been under the control of moderate militias from the western city of Zintan, which took control of it three years ago during the Libyan revolution, which toppled longtime dictator Moammar Gadhafi.

The takeover of the airport followed a more than a monthlong offensive dubbed "Libya Dawn," the alliance said on social media.

Nearly three years after a revolution and NATO military intervention, Libya continues to be beset by instability -- politically, militarily and otherwise. That has included extensive violence, much of it involving increasingly powerful militias that have outgunned the North African nation's central government.

Late last month, the U.S. Embassy in Tripoli, the United Nations and other international organizations and businesses evacuated their staffs due to the unrest.

The airport in Tripoli has long been a focal point of this fighting, as fighters tried to wrest control of it from the Zintan militia.

The head of Libya's U.N. mission, Tarek Mitri, said in July that the stakes were high for all sides.

"As the number of military actors mobilizing and consolidating their presence within the capital continues to grow, there is a mounting sense of a probable imminent and significant escalation in the conflict," Mitri said.