Malaysian Prime Minister Najib Razak said the movements of the missing jet were consistent with "deliberate action" by someone on board and the authorities have refocused their investigation on its crew and passengers.

"Based on new satellite communication, we can say with a high degree of certainty that the aircraft communications addressing and reporting system, or ACARS, was disabled just before the aircraft reached the east coast of Peninsula Malaysia," he told a press conference near the capital's International Airport.

Citing Malaysian air force radar data, the prime minister said the missing flight did indeed turn back, then flew westward back over Peninsula Malaysia before turning northwest.

"These movements are consistent with deliberate action by someone on the plane," he said.

The prime minister said the Malaysian authorities are now trying to trace the missing jet in one of the two possible corridors, a northern corridor from the border of Kazakstan and Kukmenistan to northern Thailand, and a southern corridor stretching from Indonesia to the southern Indian Ocean.

The Malaysian authorities are also working with other countries to gather all information relevant to the search, including radar data and keep the relevant countries updated about the search mission, especially those countries that have passengers on board the plane.

"Clearly, the search for MH 370 has entered a new phase," the prime minister said.

Flight MH370, on an overnight flight from Kuala Lumpur to Beijing, relayed no distress signal, indications of rough weather, or other signs of trouble.

Contact with the flight was lost along with its radar signal at 2:40 a.m. Beijing time on Saturday when it was flying over the Ho Chi Minh air traffic control area in Vietnam.

(Xinhua News Agency March 15, 2014)