Malaysia's prime minister, Najib Razak, says there is a "high degree of certainty" someone deliberately shut off the communications systems on the missing Malaysian jetliner, but he stopped short of saying the plane was hijacked.
Mr. Najib's remarks Saturday triggered a new flood of speculation into what caused the Boeing 777 to vanish from civilian radar soon after taking off on March 8.
He said somewhere near the Malaysian border the plane's transponder was switched off, before the jet veered westward in a fashion "consistent with deliberate action."
"The Royal Malaysian Air Force primary radar data showed that an aircraft, which was believed, but not confirmed to be MH370 did indeed turn back. It then flew in a westerly direction back over peninsula Malaysia before turning northwest."
The prime minister said despite media reports of a hijacking, Malaysian authorities are looking into all possibilities of what might have caused the flight to deviate from its original path. He said officials are refocusing their investigation on the crew and passengers.
Mr. Najib said signals between the Malaysia Airlines plane and a satellite continued more than six-and-a-half hours after primary contact with the jet was lost.
He said authorities are now trying to trace the plane in two possible corridors: one from the border of Kazakhstan to northern Thailand, and the other south to the southern Indian Ocean. He said search efforts in the South China Sea are ending.
The disappearance of Malaysia Airlines Flight 370 has led to one of aviation's most puzzling mysteries.
Speculation has been rampant about what caused the plane's disappearance, including mechanical failure, a hijacking, terrorism or pilot intent to commit suicide.
Dozens of ships and planes from about 15 countries have contributed to the search for the aircraft, which had 239 people on board. It was flying from Kuala Lumpur to Beijing when it disappeared.
U.S. officials have said the jet may have crashed into the Indian Ocean. Indian military aircraft have flown in the Indian Ocean over the Andaman and Nicobar Islands -- more than 500 mostly uninhabited, heavily forested land masses.
About two-thirds of the people on board the missing flight were Chinese. Other passengers included Europeans and Americans.