US officials say Egypt and the UAE were behind air strikes in Libya last week that targeted Islamist militia.
A senior US official told the BBC that Washington was not consulted about the attacks and was “caught off-guard”.
The air strikes on militia positions around Tripoli’s international airport were reportedly carried out by Emirati fighter jets using bases in Egypt.
The Egyptian authorities have denied involvement, and there has been no direct comment from the UAE.
The strikes failed to stop militias from Misrata and other cities, which operate under the banner Libya Dawn and include some Islamist groups, seizing the airport from a militia from Zintan that had controlled it since 2011.
The BBC’s Rana Jawad in Tripoli says the Misrata alliance is now effectively in control of the capital because their rivals have withdrawn from the city.
She says that life has largely come to a standstill, with many business and offices closed, while many residents are afraid.
Hundreds of people have died during more than a month of fighting which has left the airport in ruins.
What US officials have described as a pair of air strikes in and around Tripoli airport by jets from the United Arab Emirate is remarkable for a number of reasons.
Firstly the fact that the small Gulf state – staging from an airfield in Egypt – carried out the attacks at all.
This is very unusual – a mark of the growing unease of the region’s traditional rulers at the upheavals prompted by radical Islamists.
Secondly there is the fact that neither the UAE, nor Egypt, told Washington in advance. It is a measure of the declining standing in the region of the Obama administration, which is widely seen as hesitant and vacillating.
Of course, the US was significantly involved in the operation to oust Libya’s former regime, but since then, neither it nor its partners like Britain and France, have shown much ability to influence events on the ground.
The official told the BBC that the US had not been consulted about the air strikes and that it was concerned that US weapons may have been used, violating agreements under which they were sold.
A report in The New York Times on Monday said the UAE had provided the military aircraft, aerial refuelling planes and crews while Egypt gave access to its air bases.
