Malaysia said Sunday the number of countries searching for a missing airliner had nearly doubled to 25 as a full-scale criminal probe into its disappearance got under way, with particular scrutiny of the pilots.

Transport Minister Hishammuddin Hussein said the number of participating countries had jumped from 14 to 25 as the search for the aircraft focused on two vast, and vastly contrasting, land and ocean transport corridors. The dramatic "re-calibration" will inevitably bring "new challenges of coordination and diplomacy", the minister said.

Malaysian police said they had searched the homes of both pilots and examined the captain's home flight simulator after it became increasingly clear that the Malaysia Airlines Boeing 777 that vanished March 8 had been deliberately diverted by someone on board.

Experts said it would have taken specialist knowledge to disable the communications system, intensifying scrutiny of Captain Zaharie Ahmad Shah and his First Officer, Fariq Abdul Hamid.

US intelligence is also focusing on the pilot and co-pilot, a key US lawmaker said.

"One thing we do know, this was not an accident. It was an intentional, deliberate act, to bring down this airplane. And the question is who is behind that," Michael McCaul, the chairman of the House Homeland Security Committee, told Fox News.

Friends and colleagues of both pilots have testified to their good character, but questions have been raised over the flight simulator Zaharie installed at home -- even though aviation commentators have said this is not uncommon.

It also emerged that Zaharie had close ties with the party of Malaysian opposition leader Anwar Ibrahim, who has been battling a charge of sodomy.

A day before the flight, a Malaysian court overturned Anwar's 2012 acquittal on charges he sodomised a male former aide and sentenced him to five years in jail.

But authorities have not disclosed whether Zaharie's political affiliations figured in the investigation.

Fariq's record was queried after a woman said he had allowed her and a friend to ride in the cockpit of an earlier flight.

Hishammuddin noted that the two pilots "did not ask to fly together" on the missing plane.

- New search parameters -

The transport minister cautioned against "jumping to conclusions" about the thrust of the investigation, which national police chief Khalid Abu Bakar stressed was covering all 239 passengers and crew.

Engineers who may have had contact with the aircraft before takeoff were also being looked at, Khalid said.

The police action followed Saturday's startling revelations that the plane's communications systems had been manually switched off before the jet veered westward and flew on for hours.

Like Prime Minister Najib Razak the previous day, Hishammuddin refused to use the word hijacking, saying only that the pattern of events was consistent with "deliberate action" by someone on the plane.

The new search parameters involve two possible flight corridors -- a northern one stretching from Thailand to Kazakhstan and a southern one from Indonesia towards the southern Indian Ocean.

The Malaysian foreign ministry briefed representatives from 22 countries on Sunday, including the central Asian states of Kazakhstan, Uzbekistan, Kyrgyzstan and Turkmenistan, and requested support in the form of satellite and radar data.

For anguished relatives, the news the plane had been diverted was a double-edged sword -- holding out the slim hope that hijackers had landed the plane somewhere, while ushering in another agonising open-ended waiting period.

- 'What did they put up with?' -

Relatives of Bob and Cathy Lawton, a missing Australian couple, said they were horrified by the notion of a drawn-out hijack ordeal.

"That's one of the worst things I could have hoped for," Bob's brother David Lawton told News Limited newspapers.

"Even if they are alive, what did they have to put up with?"

The scope for speculation is as broad as the new search area.

Beyond the scrutiny of the cockpit crew, the possibility that the cockpit was taken over or the pilots were coerced opens a Pandora's Box of possibilities as to who might have been involved and why.

Two passengers who boarded the plane with stolen EU passports have been identified as Iranians by Interpol, who said they were most likely illegal immigrants who did not fit terrorist profiles.

The fact that most of the passengers on board the Beijing-bound flight were Chinese has raised speculation of involvement by militants from China's Muslim ethnic Uighur minority.

Security experts warned against reading too much into partial data.

"We still really don't have a lot of evidence to go on," said Anthony Brickhouse, a member of the International Society of Air Safety Investigators.

"We don't have any wreckage, we don't have the plane itself, we don't have a lot of electronic data from the aircraft."

The last satellite communication from the plane on March 8 came nearly eight hours after it took off -- around the time the airline has said it would have run out of fuel.

Hishammuddin said both search corridors were being treated "with equal importance", but a number of analysts said the southern ocean route was more likely.

Flying along the northern corridor would have required the plane to travel undetected through numerous national airspaces in a strategically sensitive region.

"I just can't think of a scenario where this aircraft is sitting on a runway somewhere," Brickhouse said.

Scott Hamilton, managing director of US-based aerospace consultancy Leehman Co, said a crash in the ocean would present a daunting search and recovery challenge.

"Any floating debris will be widely dispersed and the main debris on the sea floor," he said.

Malaysia under fresh fire over handling of plane crisis
Beijing (AFP) March 16, 2014 - China spearheaded fresh criticism Sunday of Malaysia's handling of a missing airliner drama, saying it "squandered" precious time and resources by releasing dramatic information on the plane's fate a full week after it vanished.

Prime Minister Najib Razak revealed a day earlier that an investigation indicates Malaysia Airlines flight 370 was deliberately diverted and flew for several hours after leaving its intended flight path.

He stopped short of saying it was hijacked, but the news indicates the plane had not crashed or blow up shortly after take-off as widely feared, but that something more sinister was afoot.

The startling revelation after a week of confusion and competing theories prompted questions over why it took Malaysian authorities so long to reveal the new data, and whether they had missed an opportunity to intercept the diverted plane.

"It is undeniable that the disclosure of such vital information is painfully belated," a scathing editorial by China's state-run Xinhua news agency said, noting the "excruciating" seven days it entailed for relatives of the missing.

It suggested Malaysian officials were guilty of an "intolerable" dereliction of duty.

Two-thirds of the passengers on board the flight from Kuala Lumpur to Beijing were Chinese.

There was particular anger and frustration that Malaysia had taken so long to cancel massive search operations by several countries in the South China Sea if it already knew the plane appeared to have doubled back and flown towards the Indian Ocean.

Najib did not announce the end of search operations in the South China Sea until Saturday. The plane disappeared off civilian radar over the South China Sea between Malaysia and Vietnam on March 8.

"And due to the absence -- or at least lack -- of timely authoritative information, massive efforts have been squandered, and numerous rumours have been spawned," the editorial said.

- 'Astonishing failure' -

Najib revealed Saturday that the Boeing 777's communications systems were switched off -- one after the other, suggesting a conscious act -- before the jet veered westward, flying onward for several hours either south into the Indian Ocean or north towards South and Central Asia.

"As the leader of the international search and rescue mission, Malaysia bears inescapable responsibility," the editorial said.

Similar outrage was vented on Malaysia's active social media, and on Weibo -- China's version of Twitter.

"The Malaysian government's behaviour in this affair can be summed up in one word: 'deceptive'," said one typical Weibo comment.

Immigration officials also were embarrassed by revelations that at least two people used stolen European passports to board the plane. Interpol has said they were believed merely to be illegal migrants trying to reach Europe.

Malaysia air force chief General Rodzali Daud admitted early in the drama that an unidentified object -- now determined to have been MH370 -- was plotted moving across Malaysia and toward the Andaman Sea.

He said at the time it was not intercepted because it was not deemed "hostile".

Malaysia has denied there was any lapse in its air defense, as well as accusations it was slow to share information due to national security concerns, saying it needed days to "corroborate" radar data before going public.

But security and aviation experts continued to question why so many resources were deployed in searching the South China Sea for so long, and how the Malaysian military had failed to identify the plane as it crossed back over the country.

"It is an astonishing failure of security," said Ajaj Sahni, executive director of India's Institute for Conflict Management in New Delhi.

"And it seems an astonishing failure of technology in every aspect that something like this could happen."

Terence Fan, an aviation expert at the Singapore Management University, said Malaysia's crisis management was flawed and had tested public confidence.

"Why did they need days to 'corroborate' from their own radar images that the airplane could have turned west?" Fan said.

"Couldn't they have known from day one that the different communications systems on the aircraft were turned off at different times?" he added.

Questions also have been raised over why it took Malaysian authorities a full week to search the home of the pilot and co-pilot after such a baffling disappearance.

No information has yet emerged to implicate either of the men.