TRIPOLI - Fierce clashes broke out in the Libyan capital on Monday, killing at least 20 people, shutting the airport and damaging planes during what the government said was a failed attempt to spring militants from a nearby prison.

The attack triggered the heaviest fighting in Tripoli for months, undercutting claims by the internationally recognized Government of National Accord to have largely stabilized the city. The violence also undermines GNA efforts to persuade diplomatic missions to return there.

Automatic gunfire and artillery rounds could be heard from the city center early in the day and authorities at Mitiga airport, which operates all civilian air traffic to and from the capital, said flights had been suspended until further notice.

The airport was empty in the afternoon, when the clashes had largely died down, though pilots flew several aircraft across the capital to the international airport - closed since 2014 due to damage from earlier fighting - in an effort to protect them.

A reporter saw one Airbus A319 operated by Afriqiyah Airways sitting in a hangar at Mitiga with a hole in its roof from artillery fire.

At least four other aircraft suffered what appeared to be lesser damage from gunfire.

The fighting pitted the Special Deterrence Force, or Rada, one of Tripoli's most powerful armed groups, against a rival faction based in the city's Tajoura neighborhood.

Rada acts as an anti-crime and anti-terrorism unit and controls Mitiga airport and a large prison next to it. It is aligned with the GNA and is occasionally targeted by rivals whose members it has arrested.

Rada said the airport had been attacked by men loyal to a militia leader known as Bashir 'the Cow' and others it had been seeking following their escape from a prison it controls elsewhere in Tripoli.

The GNA said the attack had "endangered the lives of passengers, affected aviation safety and terrorized residents".

Mitiga is a military air base near the center of Tripoli that began hosting civilian flights after the international airport was put out of service in 2014. In an adjacent prison, Rada says it is holding some 2,500 people, including IS suspects.

Tripoli has been controlled by a patchwork of armed groups since a 2011 uprising that toppled longtime leader Muammar Gadhafi and led to the splintering of the country. There have been rival governments in Tripoli and the east since 2014, when most diplomatic missions evacuated to neighboring Tunisia.

Reuters - Xinhua