"Based on new satellite communication, we can say with a high degree of certainty that the aircraft communications, addressing and reporting system were disabled just before the aircraft reached the east coast of peninsular Malaysia," he said at a press conference here.
"Shortly afterward, near the border between Malaysian and Vietnamese air traffic control, the aircraft's transponder was switched off."
From this point onwards, the Malaysia air force radar data showed an aircraft, which was believed but not confirmed to be the missing jet, did indeed turn back, and flew in a westerly direction, back over peninsular Malaysia before turning northwest, Xinhua quoted Razak as saying.
"These movements are consistent with deliberate action by someone on the plane," he added.
Malaysia Airlines flight MH370 with 239 passengers and crew on board mysteriously vanished about an hour after taking off from Kuala Lumpur early morning on March 8. The Boeing 777-200ER was initially presumed to have crashed off the Vietnamese coast in the South China Sea.
The plane took off from Kuala Lumpur at 12.41 a.m. on March 8 and was due to land in Beijing at 6.30 a.m. the same day. The 227 passengers on the flight included five Indians, 154 Chinese and 38 Malaysians.
Contact with the plane was lost along with its radar signal at 1.40 a.m. March 8 when it was flying over the air traffic control area of Ho Chi Minh City in Vietnam.
Based on the new data, the aviation authorities of Malaysia and their international counterparts have determined that the plane's last communication with the satellite was in one of the two possible corridors - a northern corridor stretching approximately from the border of Kazakhstan and Turkmenistan to northern Thailand, or a southern corridor, stretching from Indonesia to the southern India Ocean.
In view of this latest development, the Malaysian authorities have refocused their investigation into the crew and passengers on board the plane.
"Despite media reports that the plane was hijacked, I wish to be very clear, we're still investigating all possibilities as to what caused MH370 to deviate from its original flight path," he said.
Malaysian authorities have decided to end the search operation in the South China Sea and shift the focus of search efforts to the Indian Ocean, Razak added.
A multinational intensive search operation has so far failed to locate the plane.
According to an earlier Xinhua report that cited an unnamed official, investigators concluded that the missing Malaysia Airlines flight MH370 might have been hijacked.
According to the report, which was not corroborated, the hijackers had rich flying experience and they switched off communication devices deliberately and steered the Boeing 777 aircraft off course.
Although piracy is no longer a theory, the motives are yet to be established, the official was quoted as saying.