Malaysia Airlines plane that has been missing for more than 24 hours may have turned back, radar signals showed.
Rescue teams looking for the plane have now widened their search area.
Investigators are also checking CCTV footage of two passengers who are believed to have boarded the plane using stolen passports.
Flight MH370 from Kuala Lumpur to Beijing disappeared south of Vietnam with 239 people on board.
Air and sea rescue teams have been searching an area of the South China Sea south of Vietnam for more than 24 hours.
Malaysia’s civil aviation chief, Azharuddin Abdul Rahman, told a press conference in Kuala Lumpur the search area had been expanded, to include the west coast of Malaysia.
Five passengers booked on the flight did not board, he added. Their luggage was consequently removed.
Twenty-two aircraft and 40 ships are now involved in the search, armed forces chief Gen. Zulkefli Zin said.
Air force chief Rodzali Daud said the investigation was now focusing on a recording of radar signals that showed there was a “possibility” the aircraft had turned back from its flight path.
Vietnamese navy ships which reached two oil slicks spotted earlier in the South China Sea found no signs of wreckage.
Malaysia’s Transport Minister, Hishammuddin Hussein, initially said at least four names on the passenger list were “suspect”.
However, he later said there were in fact only two suspect names.
Reports suggest two of the passengers listed as travelling – an Italian and an Austrian – were not actually on the flight.
They had both reportedly had their passports stolen in Thailand in recent years.
Hishammuddin Hussein said international agencies including the FBI had joined the investigation and all angles were being examined.
The passengers on the flight were of 14 different nationalities. Two-thirds were from China, while others were from elsewhere in Asia, North America and Europe.
When he was asked earlier whether terrorism was suspected as a reason for the plane’s disappearance, Malaysian PM Najib Razak said: “We are looking at all possibilities but it is too early to make any conclusive remarks.”
Malaysia Airlines plane vanished at 01:30 local time on Saturday, March 8.
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