Egypt and the United Arab Emirates were responsible for carrying out two series of airstrikes in the past week on armed Islamist factions in Tripoli, 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 airstrikes or other military operations in Libya.