The U.S. was "caught off guard" by air strikes against Islamist militia in Libya, according to BBC News.

The attacks on militia positions around Tripoli airport were reportedly carried out by the United Arab Emirates (UAE) from bases in Egypt. The latter has denied any involvement and the UAE has not commented, the BBC says.

A militia alliance recently captured the capital's international airport after a battle lasting nearly a month.

A senior official told the BBC that the U.S. had not been consulted about the air strikes and that it was concerned that U.S. weapons may have been used, violating agreements under which they were sold.

The unidentified war planes attacked twice in the past week during a battle for Tripoli's airport between Islamist and nationalist militias.

A report in The New York Times on Monday, Aug 25, said the UAE had provided the military aircraft, aerial refuelling planes and crews while Egypt gave access to its air bases.

On Monday, the U.S., France, Germany, Italy and the UK issued a joint statement denouncing "outside interference" in Libya which it said "exacerbates current divisions and undermines Libya's democratic transition".

Violence in Libya has surged recently between the rival groups who overthrew Muammar Gaddafi in the 2011 uprising. Libya's police and army remain weak in comparison with the militias.

Over the weekend, Islamist-affiliated forces from Misrata and other cities took over Tripoli airport from the Zintan militia, which has held it for three years.

The airport, Libya's largest, has been closed for more than a month because of the fighting. Hundreds of people have died since clashes broke out in Tripoli in July.

In another development on Monday, Libya's previous Islamist-dominated parliament reconvened and voted to disband the country's interim government.

Elections in June saw the old General National Congress (GNC), where Islamists had a strong voice, replaced by the House of Representatives, dominated by liberals and federalists.

The GNC, which reconvened in Tripoli on Monday, has refused to acknowledge the legitimacy of its successor assembly, which is based in Tobruk.

The House of Representatives says the groups now in control of Tripoli airport are "terrorist organizations".

But the Misrata-led brigade, now in control of Tripoli airport, has called on the GNC to resume work.

Libya's government has repeatedly called for the militia groups to disband and join the national army. But so far, few have shown a willingness to disarm.