The disappearance of Malaysia Airlines Flight MH370 was most likely not due to a terrorist attack, the secretary-general of international police agency Interpol said Tuesday.
"The more information we get, the more we are inclined to conclude it is not a terrorist incident," Ronald K. Noble told reporters.
"The focus of the world right now and of law enforcement … should be on trying to find the plane and hopefully find survivors, as difficult as they might be to believe that might occur, and to helping support the investigation on the ground," he said of the 239 people aboard.
He said the two passengers with stolen passports were Iranians who had swapped their passports in Kuala Lumpur and used stolen Italian and Austrian passports to board the missing plane.
Noble's news conference came hours after Malaysia's police chief said the investigation into the missing Malaysian Airlines flight was focused on four main areas that include personal and psychological problems, as the search effort for the missing jet expanded its reach.
Inspector General Khalid Abu Bakar identified one of the individuals with a stolen passport as Pouria Nour Mohammad Mehrdad. The police chief said he was unlikely to have links to a terrorist group and was probably migrating to Germany.
Noble identified the other Iranian as Delavar Seyedmohammaderza, 29.
Both bought their tickets in Thailand and entered Malaysia together, The Associated Press reported.
The airline says the pilots did not send any distress signals, suggesting a sudden and possibly catastrophic incident. Speculation has ranged widely about possible causes, including pilot error, plane malfunction, hijacking and terrorism.
"We are looking at all areas," Abu Bakar said, referring to the police investigation. "There are four main areas we are focusing on: hijacking, sabotage, personal problems among the crew and passengers and psychological problems among the crew and passengers."
Asked what he meant by personal problems, the inspector general said: "There may be somebody there on the flight who has bought huge sums of insurance and wants the family to gain. We are looking into all possibilities at this stage."
More than 70 aircraft and ships are involved in the search for the Boeing 777, which lost contact with air traffic control en route to Beijing from Kuala Lumpur on Saturday.
(Read more: Why a high-tech jet is so hard to find)
"There are no traces and no objects that we have picked up from the sea that comes from the aircraft concerned," Azharuddin Abdul Rahman, director general of Malaysia's Civil Aviation Department, told CNBC in a telephone interview.
"I hope everybody will stay patient, we are doing our work, we are intensifying our search and we will not stop until we find something from the aircraft," he added.
The search area has been expanded to 100 nautical miles in the Gulf of Thailand, off Malaysia's east coast. The Straits of Malacca off the west coast, is also being searched, Abdul Rahman said.
Amid reports about possible sightings of debris, one compelling lead turned out to be inconclusive. Malaysian authorities said late Monday that oil slicks spotted off South Vietnam were not connected to the missing plane.
"We have inputs around the world from satellite images. So far we have received two reports this morning," said Azharuddin, adding the reports have proved inconclusive.
In a statement, Malaysia Airlines said the focus of the search was now in the west peninsula of Malaysia and the Straits of Malacca, while authorities are looking at the possibility that Flight 370 attempted to turn back.
"All angles are being looked at. We are not ruling out any possibilities," the statement said.
Search and rescue
"The mere fact that this is still a search and rescue [operation] rather than a disaster underlines how uncertain the authorities are as to what could have happened to this airplane," Alistair Newton, senior political analyst at Nomura, told CNBC.
Malaysia's chief investigator told CNBC he could not say at this stage whether the nature of the operation would change from search and rescue.
"We have to have a very deep analysis of what is going on, what is expected for the next few days," Azharuddin said.
Flight 370 disappeared about an hour into its flight from Kuala Lumpur, after climbing to a cruising altitude of 35,000 feet.
The aircraft was carrying 227 passengers and 12 crew members. Among them were 14 nationalities, including at least 152 Chinese, 38 Malaysians, seven Indonesians, six Australians, five Indians, four French and three Americans, according to Malaysia Airlines.
"It's actually beyond perplexing," said Mark Weiss, civil aviation lead at defense consulting firm The Spectrum Group. "I did fly the Boeing 777.... I am very familiar with the aircraft, and being familiar with the aircraft I am very uncomfortable, that airplane just doesn't fall out of the sky."
(Read more: Passports are weak link in overseas airports)
Focus on emergency transmitter
Experts voiced their concern that no signal from the aircraft's emergency beacon had been located.
"The emergency locator transmitter is probably continually pinging now. It's perhaps in a great depth of water, and the search is located far afield if they are not currently locating that," said Weiss.
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"If you remember what happened on the Air France 447 flight, it was a number of days before they found wreckage and it was quite some time before they were able to get the pinging from the electronic transmitter," he added, referring to the Air France flight that went missing over the south Atlantic in 2009.
Assistance teams from the U.S. National Transportation Safety Board, Boeing and U.S. Federal Aviation Administration arrived in Malaysia on Monday to help in the investigation.
"They [the NTSB team] would work in conjunction with them [Malaysian authorities] in trying to determine a trajectory pattern based on whatever radar info is available and try to narrow down a search area to the most likely places." said Greg Feith, a former senior air safety investigator at the NTSB in Denver.
— By CNBC.com. Follow us on Twitter @CNBCWorld. The Associated Press contributed to this story.