UAE air strikes on Libya aim to prevent Islamists from controlling the violence-stricken country and sends a message to Washington that it is capable of protecting its own interests, experts say.

United States officials said that United Arab Emirates warplanes secretly bombed Islamist militia targets in Libya from bases in Egypt last week, but Abu Dhabi has not publicly acknowledged involvement. On Tuesday, Egypt denied any "direct" role in the raids.

Libya has plunged into chaos since the overthrow in 2011 of long-time dictator Moamer Kadhafi, with deadly clashes between Islamist and nationalist militias.

The crisis deepened on Monday when the North African country's Islamist-dominated General National Congress named a premier-designate to form a rival administration to the interim government, which is struggling to enforce security.

American officials have confirmed that United Arab Emirates' jets launched two raids in seven days, upping the ante by regional Arab states that have previously fought proxy wars in Libya, Syria and Iraq in a struggle for power and influence.

Britain, France, Germany, Italy and the United States issued a joint statement saying that "outside interference in Libya exacerbates current divisions and undermines Libya's democratic transition".

"I think this strike is the unsurprising result of a momentum we've seen building in Libya... and within the region amongst Egypt and these Gulf states," said Frederic Wehrey of the Carnegie Endowment for International Peace.

"I believe there was no consultation with the West," added Wehrey, a specialist on the Gulf, Libya and American policy in the Middle East.

Egypt, Saudi Arabia and the UAE view Muslim Brotherhood militants in the region as a serious threat and have forged cooperation against what they see as a common danger.

With the eyes of Western powers focused on Iraq and Syria, Egypt and the UAE saw "that they had to take this kind of unusual operation," said Abdulkhaleq Abdulla, political science professor at Emirates University.

- US 'no longer reliable' -

The air strikes underscored how Washington's old allies are willing to act without backing from the Americans.

Saudi and UAE leaders in particular have expressed concern that Washington can no longer be counted on, citing US diplomatic overtures to Iran and a cautious approach to the Syrian conflict.

"The lesson of Syria still resonates... that you cannot depend on America or the West... America is no longer reliable," says Abdulla.

Wehrey agreed: "The sense in the Gulf is that the Gulf states need to take matters into their own hands."

Rogue Libyan general Khalifa Haftar -- who is hostile to the Muslim Brotherhood -- launched an offensive in May against Islamists in the second city of Benghazi. Wehrey, who visited Libya recently, said there was "speculation" that he was receiving "foreign backing".

Haftar, who "models himself after (President Abdel Fattah) al-Sisi in Egypt", emerged as "a local ally in Libya" to the UAE and Egypt, said Wehrey.

"Egypt is obviously worried about the rise of the Muslim Brotherhood on its border" and concerned about movements of weapons as well as jihadists that could cross its border from Libya.

The UAE, a US ally, backed Sisi's overthrow of his Islamist predecessor Mohamed Morsi -- Egypt's first elected president. It has jailed dozens of Islamists and its media and officials often criticise the Muslim Brotherhood.

- 'Combined operation' -

Abdulla said the air strikes "would not have happened if Egypt had not cooperated, and probably Saudi Arabia" too.

He agreed with Wehrey that Egypt is particularly concerned "that Libya might turn into a jihadist centre".

Militarily, Wehrey suggested that the Emirati air force led the strikes with logistical support from Egypt. "It was a combined operation," he said.

The Emiratis are "also concerned about the role of Qatar, their rival, inside Libya," he added.

Qatar also participated in the anti-Kadhafi campaign in 2011. However, the Gulf neighbours, whose relations are overshadowed by unprecedented tensions, have backed rival factions in Libya and continue to do so, experts say.

"Qatar is backing the Islamist Brotherhood factions in Libya with weapons and... the Emiratis would feel compelled to step up their involvement," says Wehrey.

For Abdulla, Emirati strikes in Libya are "a sign of confidence on the part of the UAE" which seems to be adopting a "hard power" policy after having projected itself as "soft".

"It will destabilise Libya more," he said.