TRIPOLI, Libya — Islamist militias attacked the rival Zintan group that controls Libya’s international airport in Tripoli on Sunday, triggering fierce clashes that halted flights, officials said.

The exchanges with heavy weapons, that rival armed groups retain from the 2011 NATO-backed uprising which toppled longtime dictator Moamer Kadhafi, were heard in the city center, 25 kilometers (15 miles) away, AFP correspondents reported.

An airport official said “rockets struck inside the airport perimeter around 6 am (0400 GMT)” interrupting flights.

“Clashes followed between the Zintan militia who control the airport and rivals who want to drive them out,” the official added.

The former rebel militia from Zintan, a hill town southwest of the capital, are the main supporters of liberals in parliament who are trying to resist attempts by powerful Islamists bidding for power in the vacuum left by Kadhafi’s ouster.

The attack was claimed by the Operations Cell of Libyan Revolutionaries, a coalition of Islamist militias considered the armed wing of Islamists within the General National Congress or parliament.

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

The fighting comes weeks after a contested general election to replace the Islamist-dominated General National Congress which has been mired in controversy and accused of hogging power.

Libya, awash with weapons since the end of the 2011 uprising, has also been plagued by growing lawlessness while on the political front rivals cabinets are jostling for power.

The 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.

“We affirm our support for Libya’s democratic transition and urge the seating of the new Council of Representatives as soon as possible,” she added.

She insisted that drafting a new constitution “must advance without interference or violence.”

But on Sunday of last week Libya’s electoral commission scrapped the results from 24 polling stations citing fraud.

It also announced that final results from the June 25 vote would be not announced until later this month and would cover only 184 of the 200 seats in the new GNC.

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