A terror probe involving the FBI and counterterrorism units from around the world was launched on Sunday into the disappearance of a missing Malaysia Airlines jet, as officials said they were investigating four people on the Boeing 777 flight from Kuala Lumpur to Beijing.
More than 36 hours after the last contact with flight MH370, the entire passenger list was being scrutinised as Malaysian officials worked to verify the identities of all those on board.
Foreign ministries earlier revealed that at least two tickets on the flight had been booked with stolen passports.
The passenger manifest issued by the airline included the names of two Europeans - Austrian Christian Kozel and Italian Luigi Maraldi - who, according to their foreign ministries, were not on the plane. Both had apparently had their passports stolen in Thailand during the past two years.
The BBC reported that the men using their passports had purchased tickets together and were flying on to Europe from Beijing, meaning they did not have to apply for a Chinese visa and undergo further checks.
An employee at a travel agency in Pattaya, in Thailand, said the two had purchased the tickets there.
US and European security officials said there was no proof of foul play and there could be other explanations for the use of stolen passports.
Interpol released a statement confirming that at least two passports – Austrian and Italian – recorded in its Stolen and Lost Travel Documents database were used by passengers on board the missing flight.
The agency said the Austrian and Italian passports were added to its database after their theft in Thailand in 2012 and 2013 respectively, and that it was also conducting checks on all other passports used to board flight MH 370 which may have been reported stolen.
"At this time, Interpol is unable to determine on how many other occasions these passports were used to board flights or cross borders," the statement said.
Interpol added it was currently in contact with its National Central Bureaus in the involved countries to determine the true identities of the passengers who used these stolen passports to board the missing Malaysia Airways flight.
The Chinese Ministry of Public Security said on Sunday night that it was sending a task force to Malaysia to jointly investigate the two passengers who boarded MH370 with stolen passports, after it verified the information with Interpol, according to the official Xinhua News Agency.
Malaysia’s acting transport minister Hishammuddin Hussein said: "Counterterrorism units... from all the relevant countries have been informed."
The probe into the disappearance of the jet and 239 people continued as Malaysian military officials said radar records indicated that the flight had turned back towards Kuala Lumpur before it vanished.
Rodzali Daud, the Royal Malaysian Air Force chief, said: “What we have done is actually look into the recording on the radar that we have and we realised there is a possibility the aircraft did make a turnback."
Malaysian rescue teams this morning expanded the search for the flight, which was carrying 227 passengers and 12 crew, to the country's west coast.
It is thought to have crashed on Saturday, after losing contact with air traffic controllers.
View MH370: possible locations in a larger map
Five children aged from two to four years - two from the United States and three from China - were among the passengers, along with two French teenagers aged 14 and 17. The eldest flyer was a 79-year-old Chinese national.
The airline said Sunday it was working with a disaster recovery management specialist from the US as it resumed the desperate search for the vanisher airliner. The company said that 'in fearing the worst', it had taken on the squad of experts to assist 'in this crucial time'.
Malaysia Airlines said a "go team" had been sent to Beijing to assist family members of the passengers.
Azaharudin Abdul Rahman, deputy chief of Malaysia's Civil Aviation Authority, said on Sunday morning that three aircraft searching the site had still not yet located any sign of the plane.
In a statement the airline said: "More than 24 hours after the loss of contact with Malaysia Airlines Flight MH370, the search and rescue teams are still unable to detect the whereabouts of the missing aircraft."
Malaysia Airlines chief Ahmad Jauhari Yahya said in a statement Sunday afternoon: "As the hours turn into days, we at Malaysia Airlines are similarly anxious and we appreciate the patience, support and prayers from everyone.
"We, however, acknowledge that the most affected group in this incident is the families of those on-board. As such, our primary focus at this point in time is to care for the families. This means providing them with timely information, travel facilities, accommodation, meals and emotional support.
"Initial financial assistance has been given out to all families. Caregivers are already assigned to each family and they are trained staff and volunteers from Malaysia and Australia.
"Family members of the MH370 passengers from Beijing who wish to travel will be flown in stages to Kuala Lumpur on the available flights. We are also communicating with the families from other nations to similarly arrange for their travel to Kuala Lumpur."
In Beijing, hope is wearing thin for the family members of MH370 passengers who have waited for news of their loved ones since Saturday morning. Around 80 family members of the passengers signed a petition letter on Sunday afternoon urging Malaysia Airlines to release the “truth” behind the mysterious disappearance of MH370 by 5pm.
In the letter, family members called for China’s Ministry of Foreign Affairs to intervene and help solve the issue. They also demanded the Chinese government send officials to talk to the families and negotiate on their behalf with related parties in Malaysia.
The Exit-Entry Administration of the Beijing Public Security Bureau has announced via its official Weibo social media account that officials have initiated emergency procedures for family members without passports to apply and receive them within one hour. Officials have said all Chinese family members of MH370 passengers would be issued passports on Sunday night, and they would work with Malaysian officials to get visas for family members as soon as possible.
The Philippines has deployed three air force planes and three navy patrol ships to the area, Singapore sent a C130 Hercules aircraft and Vietnam and Malaysia also dispatched aircraft and marine rescue vessels. The destroyer USS Pinckney was en route to southern Vietnam to help.
Two Chinese warships, one Chinese Coast Guard vessel and several search and rescue ships have been scrambled to the scene, according to Xinhua.
Foreign ministry officials in Rome and Vienna confirmed on Saturday night that the names of two nationals listed on the manifest of the flight matched those of passports reported stolen in Thailand.
Italian foreign ministry officials said that Luigi Maraldi, originally believed to have boarded the plane in Kuala Lumpur, was traveling in Thailand when the Beijing-bound flight took off at just after midnight on Friday.
He had reported his passport stolen last August, said a foreign ministry functionary.
Similarly, Austrian Foreign Ministry spokesman Martin Weiss confirmed that a name listed on the manifest matched that of an Austrian passport reported stolen two years ago in Phuket, Thailand. Weiss would not confirm the identity, although Britain's Daily Mirror website named him as Christian Kozel, aged 30.
The revelations will raise questions over security at Kuala Lumpur's airport, and how the stolen passports were able to be used by people other than their rightful owners.
China Southern, who jointly shared the route with Malaysian Airlines in what is termed in the industry a 'code share', said in a statement it had sold tickets to one Austrian and one Italian.
The airline confirmed it had sold seven tickets in all, including one to a Chinese passenger, one Dutch, 2 Ukranian and one Malaysian.
Vietnamese authorities said Saturday night that planes searching for the jet had spotted two oil slicks "15 to 20 kilometres long" off the southern tip of the country and that they were sending boats to investigate.
Meanwhile a photo circulated on weibo by a Chinese banker on a flight from Beijing to Kuala Lumpur was touted as a possible sighting of debris floating on the sea.
Associated Press, Reuters