The transponders of missing Malaysia Airlines flight MH370 were turned off in “what looked like a deliberate action from somebody on board the aircraft,” Malaysia’s Prime Minister Najib Razak said Saturday.

There was, he said, a “high degree of certainty that the ACARS transmission was disabled just before the aircraft reached the east coast of peninsular Malaysia.” The aircraft’s transponder was turned off shortly after, near the border between Malaysian and Vietnamese air traffic control, said the Prime Minister.

“From this point onwards, the Royal Malaysian Air Force primary radar 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 peninsular Malaysia before turning northwest,” the Prime Minister said during a live press conference. “Up until the point at which it left military primary radar coverage, these movements are consistent with deliberate action by someone on the plane,” he continued.

Raw satellite data provided by U.K.-based Inmarsat revealed that the last communication from the aircraft was at 08:11 MYT on Saturday March 8, some seven hours after it lost radar contact. Based on the data, which was analyzed by the FAA, NTSB, AAIB and Malaysian authorities, “we can confirm that the aircraft shown in the primary radar data was flight MH370,” he said. Although the precise location of the aircraft was not transmitted, investigation teams are “making further calculations which will indicate how far the aircraft may have flown,” to help refine the search.

Search operations in the South China Sea have been ended and the focus will now move to two possible corridors: a northern corridor stretching from Kazakhstan, Turkmenistan and Thailand, and a second corridor between Indonesia and the southern Indian Ocean.

“As the two new corridors involve many countries, the relevant foreign embassies have been invited to a briefing on the new information today by the Malaysian Foreign Ministry and the technical experts,” he said.

The Prime Minister said more investigations would be pursued into the passengers and crew - although he ruled out hijacking as the number one likely reason for the aircraft’s disappearance. “I wish to be very clear: we are still investigating all possibilities as to what caused MH370 to deviate from its original flight path.”