KUALA LUMPUR, Malaysia - The Malaysian jetliner missing for more than a week was deliberately diverted and continued flying for more than six hours after severing contact with the ground, meaning it could have gone as far northwest as Kazakhstan or into the Indian Ocean’s southern reaches, Malaysia’s leader said Saturday.

Prime Minister Najib Razak’s statement confirmed days of mounting speculation that the disappearance of Malaysia Airlines Flight 370 to Beijing was not accidental. It also refocused the investigation into the flight’s 12-person crew and 227 passengers.

“Clearly the search for MH370 has entered a new phase,” Najib said at a televised news conference. “It is widely understood that this has been a situation without precedent.”

Najib stressed that investigators were looking into all possibilities as to why the Boeing 777 deviated so drastically from its original flight path, saying authorities could not confirm whether it was a hijacking. Earlier Saturday, a Malaysian official said the plane had been hijacked, though he added that no motive had been established and no demands had been made known.

“In view of this latest development, the Malaysian authorities have refocused their investigation into the crew and passengers on board,” Najib said, reading from a written statement. He didn’t take any questions.

Police on Saturday went to the Kuala Lumpur homes of the pilot and co-pilot of the missing plane, according to a guard and several local reporters. A spokesman for the Royal Malaysian Police would neither confirm nor deny the reports but said there would be a news conference today.

Malaysian police have already said they are looking at the psychological state, family life and connections of pilot Zaharie Ahmad Shah, 53, and co-pilot Fariq Abdul Hamid, 27. Both have been described as respectable, community-minded men.

Experts have previously said that whoever disabled the communication systems and then flew the jet must have had a high degree of technical knowledge and flying experience. One possibility they have raised was that one of the pilots wanted to commit suicide.

The plane departed for an overnight flight from Kuala Lumpur to Beijing at 12:40 a.m. March 8. Its communications with civilian air controllers were severed about 1:20 a.m., and the jet disappeared.

Investigators now have a high degree of certainty that one of the plane’s communications systems - the Aircraft and Communications Addressing and Reporting System - was partially disabled before the aircraft reached the east coast of Malaysia, Najib said. Shortly afterward, someone on board switched off the aircraft’s transponder, which communicates with civilian air traffic controllers.

Najib confirmed that Malaysian air force defense radar picked up traces of the plane turning back westward, crossing over peninsular Malaysia into the northern stretches of the Strait of Malacca. Authorities previously had said this radar data could not be verified.

“These movements are consistent with deliberate action by someone on the plane,” Najib said.

Although the aircraft was flying virtually blind to air traffic controllers at this point, onboard equipment continued to send “pings” to satellites.

U.S. aviation safety experts say the shutdown of communications systems makes clear the missing Malaysia Airlines jet was taken over by someone who knew how the plane worked.

To turn off the transponder, someone in the cockpit would have to turn a knob with multiple selections to the “off” position while pressing down at the same time, said John Goglia, a former member of the U.S. National Transportation Safety Board.

The Aircraft Communications Addressing and Reporting System has two aspects, Goglia said.

The information part of the system was shut down, but not the transmission part. In most planes, the information section can be shut down by hitting cockpit switches in sequence to get to a computer screen where an option must be selected using a keypad, said Goglia, an expert on aircraft maintenance.

That’s something a pilot would know how to do, but that could also be discovered through research, he said.

But to turn off the transmission portion of the system, it would be necessary to go to an electronics bay beneath the cockpit.

That’s something a pilot wouldn’t normally know how to do, Goglia said. The Malaysia plane’s transmitter continued to send out blips that were recorded by satellite once an hour for four to five hours after the transponder was turned off.

The blips don’t contain any messages or data, but the satellite can tell in a very broad way what region the blips are coming from.

Mikael Robertsson, a co-founder of Flightradar24, a global aviation tracking service, said the way the plane’s communications had been shut down pointed to knowledge of the air route.

The Boeing’s transponder was switched off just as the plane passed from Malaysian to Vietnamese air traffic control space, making it more likely that the plane’s absence from communications would not arouse attention, Robertsson said.

“Always when you fly, you are in contact with air traffic control in some country,” he said. “Instead of contacting the Vietnam air traffic control, the transponder signal was turned off, so I think the timing of turning off the signal just after you have left Malaysian air traffic control indicates someone did this on purpose, and he found the perfect moment when he wasn’t in control by Malaysia or Vietnam. He was like in no-man’s country.”

The signs indicated involvement of the crew, Robertsson said, but he emphasized that those signs were not definitive, nor did they prove whether any involvement was willing or coerced.

Malaysia’s prime minister said the last confirmed signal between the plane and a satellite came at 8:11 a.m. - 7 hours and 31 minutes after takeoff. This was more than five hours later than the previous time given by Malaysian authorities as the possible last contact.

Airline officials have said the plane had enough fuel to fly for up to about eight hours.

“The investigations team is making further calculations, which will indicate how far the aircraft may have flown after this last point of contact,” Najib said.

He said authorities had determined that the plane’s last communication with a satellite was in one of two possible arcs, or “corridors” - a northern one from northern Thailand through to the border of the Central Asian countries Kazakhstan and Turkmenistan, and a southern one from Indonesia to the southern Indian Ocean.

The northern route might have taken the plane through China, India, Pakistan, Afghanistan - which hosts U.S. military bases - and Central Asia, and it is unclear how it might have gone undetected. The region is also home to extremist Islamist groups, unstable governments and remote, sparsely populated areas.

Flying south would have put the plane over the Indian Ocean, with an average depth of 12,762 feet and thousands of miles from the nearest landmass.

Goglia said that if Malaysian military radar tracked the plane turning west, it then followed a standard route across the peninsula until it was several hundred miles offshore and beyond military radar range. Airliners generally keep to such highways in the sky to avoid colliding with other planes, but the routes are not straight lines, he said. That means it’s likely someone was still guiding the plane, Goglia said.

Britain-based aviation security consultant Chris Yates thought it was highly unlikely the plane would have taken the northern route across land in Asia.

“In theory, any country that sees a strange blip is going to get fighter planes up to have a look,” he said. “And if those fighter planes can’t make head or tail of what it is, they will shoot it down.”

U.S. officials declined to say how closely the signal allowed them to track the path of the missing plane.One U.S. official explained that the satellite wasn’t able to read the plane’s exact location or even what direction it flew. Instead, the satellite was able to determine how far the plane had traveled since the last known spot where the plane was transmitting data. That could explain how Malaysia created two possible arcs where the plane might have traveled.

Najib said search efforts in the South China Sea, where the plane first lost contact, had ended.

Indian officials said navy ships supported by long range surveillance planes and helicopters scoured Andaman Sea islands for a third day Saturday without finding evidence of the missing jet.

Two-thirds of the plane’s passengers were Chinese, and China’s government has been under pressure to give relatives firm news of the aircraft’s fate.

In a stinging commentary on Saturday, the Chinese government’s Xinhua News Agency said the Malaysian information was “painfully belated,” resulting in wasted efforts and straining the nerves of relatives.

“Given today’s technology, the delay smacks of either dereliction of duty or reluctance to share information in a full and timely manner,” Xinhua said. “That would be intolerable.”

Najib said he understood the need for families to receive information, but that his government wanted to release only fully corroborated reports. He said his country has been sharing information with international investigators, even when it meant placing “national security concerns” second to the search. U.S., British and Malaysian air safety investigators have been on the ground in Malaysia to assist with the investigation.

A foreign ministry spokesman, Qin Gang, said China would shift its search planes and ships to areas west of Malaysia. That region includes countries that have tense relations with China, including India. Qin said China would seek the cooperation of any countries affected by the redeployment.

In the Chinese capital, relatives of passengers who have anxiously awaited news at a hotel near Beijing’s airport said they felt deceived at not being told earlier about the plane’s last signal. “We are going through a roller coaster, and we feel helpless and powerless,” said a woman, who declined to give her name.

At least one of the relatives saw a glimmer of hope in word that the plane’s disappearance was a deliberate act, rather than a crash. “It’s very good,” said a woman, who gave only her surname, Wen.

Fourteen countries are involved in the search for the plane, using 43 ships and 58 aircraft.

A U.S. P-8A Poseidon, the most advanced long-range anti-submarine and anti-surface warfare aircraft in the world, was to arrive during the weekend and sweep parts of the Indian Ocean, the U.S. Defense Department said in a statement.

Information for this article was contributed by Eileen Ng, Ian Mader, Chris Brummitt, Jim Gomez, Didi Tang, Aritz Parra, Henry Hou and Joan Lowy of The Associated Press; by Keith Bradsher, Chris Buckley, Nicola Clark, Michael Forsythe, Kirk Semple, Edward Wong, Michael S. Schmidt, Emma G. Fitzsimmons and Mia Li of The New York Times; and by Chico Harlan, Ashley Halsey III, Annie Gowen, Liu Liu, Tim Craig, Joel Achenbach, Adam Goldman and Rama Lakshmi of The Washington Post.

Front Section, Pages 1 on 03/16/2014