Malaysian police said on Tuesday one of two suspect passengers who boarded a missing passenger jet was an Iranian illegal immigrant, as relatives of some of the 239 people on board said they were losing hope for a miracle.
Authorities have doubled the search radius to 100 nautical miles (equivalent to 185 kilometres) around the point where Malaysia Airlines MH370 disappeared from radar over the South China Sea early Saturday, en route from Kuala Lumpur to Beijing.
Fears of terrorism were stoked by the weekend revelation that two men boarded the flight using stolen European passports. But police said people-smuggling was emerging as the likeliest explanation for the identity fraud.
One of the pair had been identified as a 19-year-old Iranian, Malaysia's national police chief Khalid Abu Bakar told reporters.
"We believe he is not likely to be a member of any terror group and we believe he was trying to migrate to Germany," he said, adding that authorities had not yet identified the other man.
The passports – one Italian and one Austrian – were stolen over the past two years in Thailand, where police have long been battling a thriving trade in Western documents used by criminal gangs.
An Iranian man identified as "Mr Ali" made the two bookings by phone through a travel agency in the Thai resort of Pattaya on March 1, asking for the two cheapest tickets to Europe, Thai police say.
"We believe that these two passports were stolen by a human-smuggling gang who send people to work in third countries, especially European countries," Lieutenant General Panya Maman, commander of Thailand's southern region police, told AFP.
One of the tickets was from Kuala Lumpur to Frankfurt, via Beijing and Amsterdam, while the final destination for the other ticket was Copenhagen, according to travel documents seen by AFP.
China, which had 153 of its nationals on board the plane, said it would harness 10 satellites equipped with high-resolution imaging to help in the search, as Boeing said it was joining a US government team to try to unravel the mystery of what happened to its 777-200 plane.
At a hotel in Beijing where relatives are gathered, a woman surnamed Cao told AFP that her husband's brother had been on board as part of a group accompanying Chinese artists to an exhibition in Malaysia
"We feel really helpless and haven't been to sleep for days as we are very worried," she said. "We are mentally prepared for the worst."
The vastness of the search zone reflects authorities' bafflement over the plane's disappearance. On the fourth day of searching, the operation had grown to involve 41 ships and 36 aircraft from Southeast Asian countries, Australia, China, New Zealand and the United States.
The 34-year-old son of Malaysian security guard Subramaniam Gurusamy was on the flight to do business in Beijing for an oil company.
"My three-year-old grandson is asking: 'where is Dad?' We tell him father has gone to buy sweets for you," Gurusamy, 60, said as he broke down in tears.
"Please bring back my son. I am praying for divine intervention. That is the only hope we have."
Malaysian authorities and airline officials have come under fire from China for their inability to provide any indication of what happened, and for a string of contradictory statements.
But a Malaysia Airlines (MAS) statement stressed: "We are as anxious as the families to know the status of their loved ones."
The search sphere now includes land on the Malaysian peninsula itself, the waters off its west coast, and an area to the north of the Indonesian island of Sumatra.
That covers an area far removed from the scheduled route of MAS flight MH370, which officials say may have inexplicably turned back towards Kuala Lumpur.
Hapless authorities and airline officials have held a number of press conferences since the drama erupted but have had no answer for the most burning questions over whether the plane exploded, ditched in the sea, was hijacked, or any number of other scenarios.
The plane, captained by a veteran MAS pilot, had relayed no indications of distress, and weather at the time was said to be good.
Vietnam asked fishing boats off its southern coast -- where the flight dropped off radar -- for help in the effort but said it feared the worst.
"In terms of our assessments and predictions - we have little hope of a positive outcome," Pham Quy Tieu, deputy minister of transport, said Tuesday.
Emotions were running high after China's state media blamed Kuala Lumpur for a lack of information. Tearful relatives of the missing Chinese passengers voiced frustration, while some clung to fading hopes.
"I hope it is a hijacking, then there will be some hope that my young cousin has survived," a man in his 20s surnamed Su said in Beijing.
"My uncle and aunt had an emotional breakdown, they are not eating, drinking and sleeping."
Conflicting information has deepened the anguish of relatives, with tests on oil slicks in the South China Sea showing they were not from the Boeing 777 and reports of possible debris from the flight also proving to be false alarms.
Malaysian embassy officials have been processing visa applications for Chinese families wanting to take up an offer from MAS to travel to Kuala Lumpur to be closer to the operation.
A team of Chinese officials from government ministries came to Malaysia, tasked with investigating the incident and helping family members already there.