TRIPOLI - Deadly clashes raged Sunday around Libya’s main international airport, closing it down, as the anti-Islamist militia that control it came under attack, airport officials said.

The exchanges of fire with heavy weapons killed at least six people and wounded 25, a health ministry official said.

It was not immediately known if civilians were among the casualties. The assault on the Zintan militia which controls the airport by the militants came after the UN pulled staff from Libya citing security reasons, and as the United States warned of further escalation.

An airport official said “rockets struck inside the airport perimeter around 6.00 am (0400 GMT)”, followed by heavy clashes between the rival gunmen. Loud explosions and heavy gunfire were heard in the city centre, 25 kilometres (15 miles) away, AFP correspondents reported.

An airport source said Zintan fighters pushed back the assailants but that clashes continued to rage around the facility, as locals reported seeing tanks deploy and smoke billowing. Authorities closed the airport for at least three days from Sunday after initially halting flights.

The former rebel Zintan militia helped topple strongman Moamer Kadhafi in the 2011 NATO-backed uprising, and is now well established in Tripoli, controlling the airport and military sites.

The heavily armed group, named after a hill town southwest of the capital, is considered the armed wing of the liberal movement jockeying for power with extremists who dominate parliament. Sunday’s attack was claimed by the Operations Cell of Libyan Revolutionaries, a coalition of militias seen as the armed wing of Islamists within the General National Congress (GNC) or parliament.

“The revolutionary forces arrive within the perimeter of Tripoli airport and clash with armed groups inside,” it said on its Facebook page.

Britain’s Minister for the Middle East Hugh Robertson in a statement urged an immediate end to the fighting and called on all parties to engage in “meaningful dialogue”.

European Union presidency holder Italy meanwhile called for United Nations-led diplomacy in Libya to aid the democratic transition.

“All too often these crises have been ignored and there has not been adequate support for transitions after regimes are toppled and we are still paying the price,” Foreign Minister Federica Mogherini told the ANSA news agency.

The fighting comes weeks after a contested June 25 general election to replace the Islamist-dominated GNC, which has been mired in controversy and accused of hogging power.

Libya, awash with weapons since the uprising three years ago, has also been plagued by growing lawlessness, while on the political front rival cabinets are jostling for power.

The embattled Tripoli government has been powerless to act and has struggled to establish a strong army and police force, allowing ex-rebels a free hand to act.

Sunday’s clashes came just hours after the United States warned that the conflict could become “widespread” unless a new parliament is seated quickly and a new constitution drafted.

“The United States is deeply concerned by the ongoing violence in Libya and dangerous posturing that could lead to widespread conflict there,” State Department spokeswoman Jen Psaki said.

On July 6, Libya’s electoral commission scrapped the election results from 24 polling stations, citing fraud, and said final results would be announced on July 20.

Commentators say liberals will fill most seats in the new parliament, unlike in the former assembly.

But the future makeup of parliament will become clear only after the formation of political blocs, since the vote was open only to “individual candidates” and lists were barred.

The mounting violence prompted the United Nations Support Mission in Libya to announce on Thursday that it was pulling out dozens of staff.

The well-armed and disciplined Zintan militia is officially under the jurisdiction of the defence ministry, and had claimed a May 18 attack on the GNC to demand its dissolution.

The group has sided with rogue general Khalifa Haftar who has launched a deadly offensive in eastern Libya, cradle of the 2011 uprising, aimed at crushing Islamist militias.