Malaysia's prime minister says there is "a high degree of certainty" that someone deliberately shut off the communications and transponder in the missing Malaysia Airlines jet with 239 people on board.

Prime Minister Najib Razak said at a news conference Saturday that search efforts in the South China Sea are ending and officials were reassessing the deployment of assets.

He added that when Flight 370 stopped communicating with satellites, it was in one of two corridors: northern from a border region of Kazakhstan to northern Thailand, or southern from Indonesia to the southern Indian Ocean. Mr. Najib said the "search has entered a new phase."

The prime minister did not say the plane was hijacked.

He said the disappearance of the aircraft was "consistent with a deliberation action," and that authorities are refocusing their investigation on the crew and passengers. He did not take questions from reporters.

U.S. officials have said the jet may have crashed into the Indian Ocean.

Flight 370 disappeared one week ago and investigators have yet to find any firm evidence of what happened.

Theories include piracy and a catastrophic mechanical failure.

Indian military aircraft have also flown over the Andaman and Nicobar Islands -- more than 500 mostly uninhabited, heavily forested land masses.

Investigators believe the plane may have flown for several hours after disappearing from radar. They say the jet was sending electronic pings to a communications satellite.

The Boeing 777 was flying from Kuala Lumpur to Beijing when it disappeared.

About two-thirds of the people on board were Chinese. Other passengers included Europeans and Americans.