KUALA LUMPUR (2ND UPDATE) -- Malaysia on Sunday launched a terror probe into the disappearance of a passenger jet carrying 239 people, investigating suspect passengers who boarded with stolen passports, as relatives begged for news of their loved ones.
The United States sent the FBI to investigate after Malaysia Airlines flight MH370 vanished from the radar early Saturday somewhere at sea between Malaysia and Vietnam, but stressed there was no evidence of terrorism yet.
Malaysian authorities also expanded their search for wreckage to the country's west coast, asking neighbouring Indonesia for help. Searches so far had concentrated on waters to the country's east, in the South China Sea.
A total of 40 ships and 22 aircraft from an array of countries including China and the US are now involved in the hunt across the two areas, officials said.
"There is a distinct possibility the airplane did a turn-back, deviating from the course," said Malaysia's air force chief, General Rodzali Daud, citing radar data.
But Malaysia Airlines (MAS) chief executive Ahmad Jauhari Yahya said the Boeing 777's systems would have set off alarm bells.
"When there is an air turn-back the pilot would be unable to proceed as planned," he said, adding authorities were "quite puzzled" over the situation.
After it emerged that two people boarded the flight with stolen European passports, Malaysia's transport minister Hishammuddin Hussein said he was looking at four suspect passengers in all.
He declined to offer details, saying authorities were examining "the entire manifest," but confirmed the US Federal Bureau of Investigation (FBI) was dispatching personnel to Malaysia.
"At the same time our own intelligence has been activated, and of course, the counter-terrorism units... from all the relevant countries have been informed," Hishammuddin said, refusing also to rule out the possibility of a hijack.
Scouring CCTV clues
A Malaysian civil aviation official said authorities still so far believe only two passengers had used stolen passports and were examining CCTV footage of them.
Flight MH370 had relayed no distress signal, indications of rough weather, or other signs of trouble. Both Malaysia's national carrier and the Boeing 777-200 model used on the route are known for their solid safety records.
The flight went missing about an hour after taking off from Kuala Lumpur, bound for Beijing. A total of 153 Chinese nationals were on board, and relatives camped out at the main international airport in China's capital bemoaned the lack of news Sunday.
"The airline company didn't contact me, it was a friend," a middle-aged woman surnamed Nan told reporters, holding back tears, after finding out her brother-in-law was on the flight.
"I can't understand the airline company. They should have contacted the families first thing," she said.
MAS insisted it was doing its best to keep relatives informed given the confusion surrounding the plane's fate.
Buddhist monks chanted prayers for the missing passengers in the departure hall of Kuala Lumpur's airport, while the airline gathered dozens of somber-looking relatives at a nearby hotel to await news.
The carrier said it was "fearing for the worst," after Vietnamese boats reached the scene of two large oil slicks detected overnight.
Search aircraft scoured the sea Sunday but had nothing more to report yet, Vietnam's army deputy chief of staff Vo Van Tuan told AFP.
The search effort involves planes and vessels from several nations with rival maritime claims in the tense South China Sea, including China, Vietnam, Malaysia, the Philippines and Singapore.
The US Navy has contributed a surveillance plane, and said the destroyer USS Pinckney was approaching the search area, which would soon be in range of its helicopters.
A Chinese coastguard vessel also was in the area, China's state news agency said.
Two European names -- reported as Christian Kozel, an Austrian, and Luigi Maraldi of Italy -- were listed on the passenger manifest but neither man boarded the plane, officials said. Both had their passports stolen in Thailand over the past two years.
The disclosure came after it emerged that two people boarded the missing flight, MH370 from Kuala Lumpur to Beijing, with stolen European passports.
China Southern, which has a code-share agreement with MAS, listed one Italian and one Austrian among its ticketed passengers on the flight. There were no other passengers of those nationalities listed on the MAS manifest.
Meanwhile, a Chinese national whose passport number was listed on the manifest did not board the plane and was still in China, China's state media reported, adding the passport was never stolen.
In Washington, a US administration official said authorities were aware of the passports issue but had "not determined a nexus to terrorism yet."
"We're still tracking the situation," the official told AFP.
A US Department of Homeland Security official told The Los Angeles Times the bearers of the stolen passports could merely have stolen or bought them on the black market.
The flight carried 227 passengers and 12 crew. A US company based in Texas said 20 of its employees were on the flight -- a dozen from Malaysia and eight from China.
Aboard the plane were 38 Malaysians, seven Indonesians and other nationalities including Australian, Indian, American, Dutch, and French.
If the worst is confirmed, it would be just the second fatal crash in the nearly 20-year history of the popular Boeing plane. A 777-200 operated by South Korea's Asiana Airlines skidded off the runway after hitting a sea wall in San Francisco last year, killing three people.
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