Military radar-tracking evidence suggests a Malaysia Airlines jetliner missing for nearly a week was deliberately flown across the Malay peninsula towards the Andaman Islands.

Two sources familiar with the investigation told Reuters that an unidentified aircraft that investigators believe was Malaysia Airlines flight 370 was following a route between navigational waypoints.

This would indicate that it was being flown by someone with aviation training - when it was last plotted on military radar off the country's northwest coast.

The last plot on the military radar's tracking suggested the plane was flying toward India's Andaman Islands between the Andaman Sea and the Bay of Bengal, the sources said.

Waypoints are geographic locations, worked out by calculating longitude and latitude, which help pilots navigate along established air corridors.

A third source said inquiries were focusing increasingly on the theory that someone who knew how to fly a plane deliberately diverted the flight, with 239 people on board, hundreds of miles off its intended course from Kuala Lumpur to Beijing.

"What we can say is we are looking at sabotage, with hijack still on the cards," said that source, a senior Malaysian police official.

All three sources declined to be identified because they were not authorised to speak to the media and due to the sensitivity of the investigation.

Officials at Malaysia's Ministry of Transport, the official point of contact for information on the investigation, did not return calls seeking comment.

Malaysian police have previously said they were investigating whether any passengers or crew had personal or psychological problems that might shed light on the mystery, along with the possibility of a hijacking, sabotage or mechanical failure.

The comments by the three sources are the first clear indication that foul play is the main focus of official suspicions in the Boeing 777's disappearance.

As a result of the new evidence, the sources said, multinational search efforts were being stepped up in the Andaman Sea and also the Indian Ocean.

A new search area for flight 370 may be opened in the Indian Ocean, the White House said.

"It's my understanding that based on some new information that's not necessarily conclusive - but new information – an additional search area may be opened in the Indian Ocean," White House spokesman Jay Carney told reporters in Washington.

India's navy has nearly doubled the number of ships and planes deployed to search for the missing aircraft

The Indian navy said six ships and five aircraft were now scouring for any sign of the vanished plane in the Andaman Sea. 

Vietnam downgrades search operation

Meanwhile, Vietnam has downgraded its search operation from "emergency to regular".

Vietnam deployed three search planes today, down from five yesterday.

The disappearance of the Malaysia Airlines plane is one of the most baffling mysteries in the history of modern aviation.

There has been no trace of the plane nor any sign of wreckage despite a search by the navies and military aircraft of more than a dozen countries across southeast Asia.

Satellites picked up faint electronic pulses from the aircraft after it went missing on Saturday, but the signals gave no information about where the jet was heading and little else about its fate, two sources close to the investigation said yesterday.

But the "pings" indicated its maintenance troubleshooting systems were switched on and ready to communicate with satellites, showing the aircraft was at least capable of communicating after losing touch with air traffic controllers.

The system transmits such pings about once an hour, according to the sources, who said five or six were heard.

However, the pings alone are not proof that the plane was in the air or on the ground, the sources said.

Malaysian authorities have said the last civilian contact occurred as the Boeing 777-200ER flew north into the Gulf of Thailand.

They said military radar sightings indicated it may have turned sharply to the west and crossed the Malay Peninsula toward the Andaman Sea.

The new information about signals heard by satellites shed little light on the mystery of what happened to the plane, whether it was a technical failure, a hijacking or another kind of incident on board.

While the troubleshooting systems were functioning, no data links were opened, the sources said, because the companies involved had not subscribed to that level of service from the satellite operator, the sources said.

Boeing and Rolls-Royce, which supplied its Trent engines, declined to comment.

Earlier, Malaysian officials denied reports that the aircraft had continued to send technical data and said there was no evidence that it flew for hours after losing contact with air traffic controllers early last Saturday.

Ships and aircraft are now searching a vast area that had already been widened to cover both sides of the Malay Peninsula and the Andaman Sea.

The US Navy was sending an advanced P-8A Poseidon plane to help search the Strait of Malacca, separating the Malay Peninsula from the Indonesian island of Sumatra. It had already deployed a Navy P-3 Orion aircraft to those waters.

US defence officials said the US Navy guided-missile destroyer, USS Kidd, was heading to the Strait of Malacca, answering a request from the Malaysian government.

The Kidd had been searching the areas south of the Gulf of Thailand, along with the destroyer USS Pinckney.

Six Indian ships deployed in search for Malaysian jet

India's navy said it has nearly doubled the number of ships and planes deployed to search the Andaman Sea for the missing jet.

Naval authorities also said Malaysia had asked India to extend its search operations further west to the Bay of Bengal, which forms the northeastern part of the Indian Ocean.

The Indian navy said six ships and five aircraft were now scouring for any sign of the vanished plane in the Andaman Sea, which surrounds India's remote Andaman and Nicobar group of islands that lie far to the country's southeast.

"We want to cover the area and it should be strictly done," Indian naval spokesman DK Sharma told AFP.

India had earlier deployed three ships and three aircraft in the search for Malaysia Airlines Flight 370 which disappeared a week ago.

The Indian ships and aircraft were looking in an area "designated" by the Malaysian navy in the southern region of the Andaman Sea, Sharma said.

The Malaysia Airlines flight, which lost contact on Saturday en route from Kuala Lumpur to Beijing, had five Indian passengers aboard.

Indian naval authorities said in a statement that the location to be searched in the Bay of Bengal lies 900km west of Port Blair, the capital of the Andaman and Nicobar.  

A naval spokesman told AFP that India was acting on Malaysia's request, but no planes or ships had yet been diverted to the new location.

He said he had no information on when the search in the Bay of Bengal would begin.