The incoming United Nations envoy for Libya warned against foreign intervention today, as the country plunges deeper into civil conflict. On Monday, US officials accused the United Arab Emirates and Egypt of secretly conducting air strikes on Islamist militias who have seized control of Tripoli airport.

Washington has expressed alarm over aerial attacks last week on positions around the airport, claiming that they were carried out by Emirati jets using Egyptian bases. US officials reportedly said they were not consulted over the strikes, which threaten to turn the already disintegrating country into a battleground for a regional proxy war.

Then today, Bernadino Leon, the UN's newly appointed special representative for Libya, said in Cairo that he did not believe that foreign intervention could halt Libya's slide into turmoil. Leon, speaking on his last trip as EU envoy for the region, said the country needed international support to back "Libyans who want to fight chaos… through a political process."

Libya's years-long power struggle has intensified in recent weeks as an alliance of fighters — including some Islamist groups — from Misrata and other cities wrested Tripoli's airport from the rival Zintan militia, loosely allied with the rogue General Khalifa Hifter, that controlled it since 2011.

Hundreds of people have died in a month of worsening violence that has reduced the airport to a burned-out shell. The controversial air strikes failed to halt the advance of the Misrata militias, who were seen dancing on the wings of airplanes in images after the fall of the airport on Saturday.

The Misrata alliance — operating under the banner Libya Dawn — is now said to be in de facto control of the entire capital after their opponents abandoned their positions. Tripoli has been left largely paralyzed with businesses closed and many residents scared to venture on to the streets. One government official said thousands had fled the city, while armed men reportedly raided and burned homes of government supporters

"They have now started burning houses and property belonging to people from Zintan, Warshafana, Warhafal and the east," one resident tweeted. "Street fighting in different places, not safe."

Libya has also been torn between two rival governments, after the previous Islamist-dominated parliament refused to recognize the legitimacy of the new assembly elected in June. The old General National Congress reconvened in Tripoli on Monday following calls from the Misrata alliance and voted to disband Libya's interim government, while the new House of Representatives, based in Tobruk, has branded those in control of the capital "terrorist groups and outlaws".

On Monday, US officials told the New York Times that the UAE had provided the military aircraft and crews for two sets of air strikes: the first on August 18 on a weapons depot and other militia positions, and the second on Saturday, targeting rocket launchers, vehicles, and a warehouse controlled by the Misrata alliance.

The officials told the newspaper that the attacks had been conducted by the two US allies without the knowledge of the US. "We don't see this as constructive at all," one senior official said.

The US, UK, France, Germany and Italy issued a joint statement condemning "outside interference" in Libya, which they said "exacerbates current divisions and undermines Libya's democratic transition."

Libya has been mired in chaos since the fall of Muammar Qaddafi in 2011, which left a power vacuum that allowed rival militias to thrive. Its police and army are no match for such groups, while the country is awash with weapons from the arsenal of the late dictator.

The unrest has destabilized the region as a whole, sending arms and fighters flooding into much of West Africa and helping to fuel conflicts in countries such as Mali and Syria. The country's lawlessness has also helped turn it into a launchpad for migrants heading for Europe by dangerous maritime routes operated by people smugglers. Over the past week, Libyan rescuers have pulled 170 bodies from a shipwreck off the coast near Tripoli, and such tragedies have become almost commonplace in Mediterranean waters.

Now, analysts fear Libya could become an arena for a battle between regional rivals, as countries such as the UAE and Egypt attempt to crush the threat from Islamist fighters backed by Qatar.

"It's clear there is a proxy war in Libya between Saudi Arabia, UAE, Egypt and Algeria on one side and Qatar and Turkey on the other side," Mohamed Eljarh of the Atlantic Council told the Middle East Eye.

Egypt has insisted it did not carry out the air strikes, though it stopped short of denying any type of involvement. The UAE has remained silent on the issue.

Doubts have also been cast on Washington's insistence that it knew nothing of the attacks.

"With as many Aegis-class ships as the US Navy has in the Persian Gulf and Mediterranean, there is no possible way the UAE could pull this off without the US knowing it," Christopher Harmer, a former Navy officer and an analyst with the Institute for the Study of War, told Foreign Policy.