Tripoli: Islamist-led militiamen stepped up their assault on Sunday on Libya’s main airport, two days after the collapse of a truce with rival ex-rebels who control the facility, a security official said.

A coalition of militias led by Islamist fighters launched an assault on Tripoli international airport, with clashes later spreading to the road leading to the capital.

“The airport was attacked this morning with mortar rounds, rockets and tank fire,” airport security official Al Jilani Al Dahesh said.

“It was the most intense bombardment so far,” since a week-old battle for control of the airport erupted on July 13.

Dahesh said the militia that controls the airport, based in Zintan, south-west of the capital, and seen by Islamists as the armed wing of liberals within the government, responded with heavy fire.

Militias have been joined by other armed groups, including the powerful Misrata Brigade, which played a key role in the 2011 UN-backed revolt that toppled and killed strongman Muammar Gaddafi.

The fighting has forced a halt to all flights and caused extensive damage to planes and airport infrastructure, with aviation officials saying Tripoli airport could stay closed for months.

Pictures posted on social media showed a Libyan Airlines plane on fire as plumes of smoke billowed over the airport.

The carrier said on its Facebook page that one of its aircraft, a Bombardier CRJ900, was destroyed.

By midday on Sunday, fighting had spread to other sites on the airport road that are controlled by the Zintan militia.

Loud explosions were heard in the city centre, 25 kilometres away, as battles raged along the airport road.

The rival sides are among several heavily-armed militias, which have held sway in the oil-producing North African nation for the past three years.

Relentless violence across Libya this year - including a war against Islamists in the east launched by a rogue general — has sparked fears of all-out civil war.

The European Union mission in Libya issued a statement on Sunday urging fighters to lay down their arms and spare civilian lives.

“The EU is concerned about the protracted conflict over Tripoli international airport and urges all parties to exercise restraint, to abide by international law and to respect civilians,” it said.

“The EU calls on all parties to find a peaceful resolution through dialogue and compromise... there is no military solution to the crisis in Libya ... the only option is a political solution and a peaceful democratic process.”

On Thursday, Foreign Minister Mohammad Abdul Aziz pleaded for UN help to build up Libya’s army and police force and to protect vital sites, including the airport and oil installations.

The fighting mirrors a deadly power struggle between liberals and Islamists in the National General Congress, Libya’s parliament and top political authority.

A new parliament was elected last month after the GNC came under repeated accusations of trying to monopolise power.

Results of the vote had been due to be announced Sunday but the electoral commission announced a delay until Monday.