WASHINGTON (Reuters) - United Airlines said late Sunday it will immediately halt all flights by its fleet of 24 Boeing 777 airplanes with the same type of engine involved in Saturday’s emergency landing in Denver. The announcement came after the Federal Aviation Administration said it would require stepped-up inspections of 777 aircraft with Pratt & Whitney PW4000 series engines after the right engine failure on United Flight 328. United said it will continue discussions with U.S. regulators “to determine any additional steps that are needed to ensure these aircraft meet our rigorous safety standards and can return to service.” The FAA had said it expected the new inspection would require some planes to be temporarily taken out of service.