Egypt and the United Arab Emirates were responsible for carrying out two series of air strikes in the past week on armed Islamist factions in Tripoli, Libya, U.S. officials said on Monday.
The officials said the two Arab countries used aircraft based in Egypt.
Earlier the New York Times reported that the two U.S. allies acted without consulting Washington, and that Egyptian officials told U.S. diplomats that Cairo was not involved. Egypt has denied conducting air strikes or other military operations in Libya.
Over the weekend, Tripoli residents said unidentified war planes attacked targets in the capital, as Libya is riven by the worst fighting since the overthrow of Muammar Gaddafi in 2011. There were also strikes on Islamist-held positions last Monday.