KUALA LUMPUR, Malaysia — Malaysia's Prime Minister Najib Razak said Saturday that communications on a Malaysia Airlines flight missing since last Saturday were disabled due to "deliberate action by someone on the plane" and that the last known signal from the airliner came more than seven hours after takeoff.

The revelation came amid an intensifying search involving dozens of planes and ships in an ever-widening area where the plane may have gone down. Military and government experts on Saturday pored over satellite and radar data that may shed light on the fate of the plane but so far there is no trace of debris.

Speaking at a news conference in Kuala Lumpur, Prime Minister Razak said investigators were making calculations to try to determine exactly how far the airliner traveled after its last point of contact.

According to new satellite data analyzed by the FAA, NTSB, AAIB and Malaysian authorities, the plane's communications from the Aircraft and Communications Addressing and Reporting System were cut off just before the aircraft reached the east coast of the peninsula of Malaysia, and the aircraft's transponder was turned off shortly thereafter, near the border of Malaysia and Vietnam, he said.

Flight MH370 departed from Kuala Lumpur for Beijing at 12:40 a.m. on March 8 with 239 people on board. A multi-national search effort involving 14 countries, 43 ships and 58 aircraft has turned up no trace of the Boeing 777, despite an expansive search that has widened with each passing day.

The last confirmed communication from the plane to a satellite was 8:11 a.m. Malaysia time, Razak said.