The missing Malaysia Airlines plane turned away from its planned route and continued to travel for an hour, before vanishing, Malaysia's military has said.
As the search for the doomed plane enters its fourth day, Malaysia's air force has said their radar suggests flight MH370 from Kuala Lumpur to Beijing flew for about 350 miles after vanishing from air traffic control screens, travelling west over the Strait of Malacca.
"It changed course after Kota Bharu and took a lower altitude. It made it into the Malacca Strait," the military official, who has been briefed on investigations, told Reuters.
While there is still no confirmation that the Boeing 777-200 crashed, aviation experts have put forward possible causes of its disappearance including a terrorist attack, extreme turbulence, human error or even suicide.
The failure of the pilots to send a distress signal has given rise to speculation there was a sudden catastrophe - possibly caused by a mechanical failure or an explosion.
The Malaysian authorities initially said flight MH370 disappeared about an hour after it took off from Kuala Lumpur International Airport (KLIA), as it flew over the South China Sea, south of Vietnam's Ca Mau peninsula.
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No distress signal or message was sent, but it is believed the plane attempted to turn back, perhaps towards Kuala Lumpur.
Malaysia has extended the massive search operation for the plane to the Malacca Strait after initially focusing on the South China Sea.
Officials still do not know what went wrong with the aircraft.
Earlier, it emerged two men travelling on stolen passports on board the plane were Iranians with no apparent links to terrorist groups, officials said.
Pouria Nour Mohammad Mehrdad, 18, is believed to have been migrating to Germany and Interpol identified the other man as Delavar Seyed Mohammadreza, 29.