Using a system that looks for flashes around the world, the Pentagon reviewed preliminary surveillance data from the area where the plane disappeared and saw no evidence of an explosion, said an American government official who spoke on the condition of anonymity because the subject matter is classified. A team of aviation experts led by the National Transportation Safety Board was on its way to the area. 
 
 If all aboard were killed, it would be the deadliest commercial airline accident since Nov. 12, 2001, when an American Airlines Airbus crashed just after takeoff from Kennedy Airport en route to the Dominican Republic. 
 
 A senior American intelligence official said law enforcement and intelligence agencies were investigating the issue of the stolen passports. American authorities were scrutinizing the flight manifest closely, the official said, noting that forged travel documents are also used routinely by smugglers and illegal immigrants. 
 
 “At this time, we have not identified this as an act of terrorism,” said the official, who spoke on the condition of anonymity Saturday because of the continuing inquiry. “While the stolen passports are interesting, they don’t necessarily say to us that this was a terrorism act.” 
 
 A European counterterrorism official said the Italian man whose passport was stolen, Luigi Maraldi, 37, called his parents from Thailand, where he is vacationing, after discovering that someone by the same name was listed on the passenger manifest. The official, who spoke on the condition of anonymity, said Mr. Maraldi reported the theft last August to the Italian police. The official said the passport of the Austrian man, Christian Kozel, 30, who is currently in Austria, was stolen about two years ago. 
 
 Image Oil slicks on the surface of the Gulf of Thailand may have been from a crash. Credit Agence France-Presse — Getty Images 
 
 The European official said that he was surprised it had been possible to check in with stolen passports at the Kuala Lumpur airport and that an alert should have popped up on the airline agent’s computer. 
 
 Operating as Flight MH370, the plane left Kuala Lumpur just after midnight, headed for Beijing. Air traffic control in Subang, a suburb of Kuala Lumpur, lost contact with the plane around 1:30 a.m. on Saturday, Malaysia’s civil aviation department said. 
 
 China Central Television said that according to Chinese air traffic control officials, the aircraft never entered Chinese airspace. 
 
 At a news conference in Beijing after the arrival of a team of employees to assist families of the passengers in China, an official of Malaysia Airlines said the missing plane had no history of malfunctions. “It was last inspected 10 days ago, well before scheduled service,” said the executive, Ignatius Ong. “It was all in top condition.” 
 
 When pressed about possible security lapses, he repeated several times that the airline had no confirmation from the Malaysian authorities that passengers had boarded with stolen passports. 
 
 Image Ahmad Jauhari Yahya, the chief executive of Malaysia Airlines, addressed the media as the search for the plane continued. Credit Samsul Said/Reuters 
 
 Malaysia, the United States and Vietnam dispatched ships and aircraft to the mouth of the Gulf of Thailand on Saturday to join an intensive search, and the state-run Xinhua news agency said China was sending a Coast Guard vessel and two naval ships. The Chinese Ministry of Transport said a team of scuba divers who specialize in emergency rescues and recovery had been assembled on Hainan, the southern island-province, to prepare to go on Sunday to the area where the airliner may have gone down. 
 
 Lai Xuan Thanh, the director of the Civil Aviation Administration of Vietnam, said on Saturday that a Vietnamese Navy AN26 aircraft had discovered oil on the surface of the water toward the Vietnam side of the mouth of the Gulf of Thailand, east of the Malaysian Peninsula. The oil is suspected to have come from the missing plane, he added. 
 
 But on Sunday, Malaysia’s defense minister, Hishammuddin Hussein, added a confusing twist, saying the plane might have gone down west of the Malaysian peninsula. “We are looking at the possibility of an aircraft air turnback,” he said without elaborating whether the plane might have changed course for mechanical reasons or a hijacking, or why the authorities suspected the plane might have reversed course. 
 
 Malaysia Airlines said the plane had 227 passengers aboard, including two toddlers, and an all-Malaysian crew of 12. According to the manifest, the passengers included 154 citizens of China or Taiwan, 38 Malaysians, seven Indonesians, six Australians, five Indians, four French and three Americans, as well as two citizens each from Canada, New Zealand and Ukraine and one each from Austria, Italy, the Netherlands and Russia — although the true nationalities of the passengers carrying the Austrian and Italian passports are still unknown. 
 
 The family of one of the Americans aboard the flight, Philip Wood, an IBM employee in Kuala Lumpur, said they had little information beyond what had been reported in the news media. 
 
 Image A distraught couple at the Beijing Capital International Airport wait for news about the missing Malaysia Airlines flight. Credit Kim Kyung-Hoon/Reuters 
 
 “We’re relying on our Lord,” Mr. Wood’s father, Aubrey, said from his home in Keller, Tex. “He’s the one who carries the load.” 
 
 The tickets to the holders of the stolen Austrian and Italian passports were sold by China Southern Airlines, which has a code share agreement with Malaysia Airlines, according to China Southern’s account on Sina Weibo, the Chinese microblog platform. China Southern said it sold five other tickets to the flight: to the Dutch passenger, the Ukrainians, and one Malaysian and one Chinese passenger. 
 
 Arnold Barnett, a longtime Massachusetts Institute of Technology specialist in aviation safety statistics, said that before the disappearance of the plane, Malaysia Airlines had suffered two fatal crashes, in 1977 and 1995. Based on his estimate that Malaysia Airlines operates roughly 120,000 flights a year, he calculated that the airline’s safety record was consistent with that of airlines in other fairly prosperous, middle-income countries, but had not yet reached the better safety record of airlines based in the world’s richest countries. 
 
 Malaysia has not been targeted in terrorist attacks in recent decades, although the 1977 crash was attributed to a hijacking. But some of the planning for the Sept. 11 attacks in the United States was done in Malaysia, which has a relatively lax visa policy. The country is a major trading nation and a natural meeting place for a variety of groups involved in illicit activities. 
 
 The plane’s disappearance came at the end of the annual National People’s Congress in Beijing, and took place at a time of rising concern in China about terrorism. Mr. Ahmad Jauhari of Malaysia Airlines said early on in a statement that there was speculation that the plane had landed safely somewhere along the route to Beijing. But in a telephone interview before reporting the sighting of the oil in the ocean, Mr. Lai expressed concern about the aircraft’s fate. 
 
 “The possibility of an accident is high,” he said. ||||| An Austrian and Italian whose names were on the passenger list of flight MH370 but not on the flight both lost their passports in Thailand. The WSJ's Deborah Kan speaks to security consultant Steve Vickers about the thriving trade of selling fake identification in Thailand. 
 
 Two people listed as being on a missing Malaysia Airlines jet weren't on the flight, and their passports had been stolen in Thailand, authorities and family members said Saturday. 
 
 The search for the plane, which disappeared on its way from Kuala Lumpur to Beijing, centered on waters off Vietnam after Hanoi said it had spotted what appeared to be large oil slicks. 
 
 Malaysia Airlines Flight MH370, with 239 people aboard, lost contact with the airline shortly into the flight early Saturday. Government and airline officials said they weren't ready to speculate about what caused the Boeing 777-200 to disappear from radar sometime after it flew away from peninsular Malaysia's east coast. Aviation analysts noted that accidents at cruising altitude over water were rare. 
 
 Families waited all day for news in a crisis center in Kuala Lumpur's airport, and 2,700 miles away in a Beijing hotel. Of the 227 passengers on the flight, the airline said, 153 were from China or Taiwan; the list also included Malaysians, Indonesians and passengers from Australia, the U.S., France, Ukraine, India and Canada. Among those on board, the airline said: two infants, and children aged 2, 3 and 4. The plane carried a crew of 12, all Malaysians. 
 
 One passenger was traveling with a stolen Austrian passport, Austria's Foreign Ministry said Saturday. A 30-year-old Austrian whose name was on the passenger list for the flight wasn't on board. His passport was stolen in Thailand in 2012, a ministry spokesman said, confirming a report in German newspaper Die Welt. 
 
 Another passenger on the list, Italian Luigi Maraldi, was also not on the plane, Italy's Foreign Ministry said Saturday. Mr. Maraldi's passport was stolen in Thailand a year and a half ago, his father said. 
 
 Malaysia Airlines had no confirmation from Malaysian authorities that stolen passports were used to board the flight, said Ignatius Ong, a member of the airline's crisis-management team. One European security official said it wasn't uncommon for passengers to board flights using stolen passports. 
 
 View Slideshow A passenger's relative Saturday at the Beijing airport as families waited for news on the missing flight. REUTERS 
 
 Vietnam's government said late Saturday it was dispatching vessels to where its aircraft had spotted what appeared to be two oil slicks that might be from the plane, 90 miles south of Tho Chu island off the Vietnamese coast. 
 
 "It's very likely that this is a sign of the missing plane," Vo Van Tuan, deputy chief of staff of Vietnam's armed forces, told reporters. Malaysia Airline's Mr. Ong said the airline hadn't concluded whether the slicks were connected with its plane. 
 
 The search effort Saturday included aircraft and vessels from Malaysia, Vietnam, Singapore and the Philippines. The U.S. Navy said it was sending surveillance aircraft from a base in Japan and a destroyer that had been conducting training and maritime-security operations in the South China Sea. 
 
 The missing plane took off about six minutes late at 12:41 a.m. Saturday local time, according to Malaysia Airlines. Normal flight time to Beijing is just shy of six hours. The flight plan would initially carry the plane diagonally over a swath of peninsular Malaysia and, within an hour or so, over a wide ocean basin that pools the Gulf of Thailand and the South China Sea. 
 
 The plane was over the South China Sea when Malaysian air-traffic controllers lost touch at 1:30 a.m., Malaysian authorities said. 
 
 Malaysia Airlines' Mr. Ong said the plane had had its last safety inspection 10 days ago and didn't have a history of malfunction. The airline had earlier said there were no reports of bad weather along the route, and the missing plane didn't send a distress signal. 
 
 Malaysia Airlines first published word that contact with the plane had been lost about one hour after the flight was scheduled to land at daybreak Saturday in Beijing. 
 
 Malaysian authorities weren't ruling out any possibilities as they worked to determine what happened to the plane, the director-general of the country's Civil Aviation Department said. Malaysian Prime Minister Najib Razak said the search would continue for "as long as it takes." 
 
 "We are all very worried. We hope everyone is safe," China's Foreign Minister Wang Yi told a news conference scheduled as part of an annual parliament meeting. "We're doing all we can to get more details." 
 
 Relatives of passengers on Malaysia Airlines Flight 370 wait for news at a hotel in Beijing. The WSJ's Josh Chin tells us how they are coping. 
 
 It is very rare for an aircraft to suffer a "catastrophic event" at cruising altitude over water, one analyst said Saturday. For today's jets, the cruise portion of flights is considered to pose significantly fewer potential hazards than approach and landing. 
 
 Jonathan Galaviz, a partner with Global Market Advisors, an aviation and leisure consulting firm, said that while such accidents are "absolutely rare," they are also the most difficult in terms of locating wreckage and cockpit voice and flight-data recorders. 
 
 He said the emphasis over the next 48 to 72 hours would likely be on search and rescue efforts. Then, sophisticated sonar equipment could be required to locate the airplane's recorders, if indeed it went down over water, he said. 
 
 Shukor Yusof, an aviation analyst at Standard & Poor's, likened the incident to the 2009 crash over the Atlantic Ocean of an Air France jetliner en route from Brazil to France, which killed all 228 people on board. "The wreckage for that aircraft wasn't recovered or rather salvaged until almost two years after," Mr. Yusof said. "It shows the tremendous challenge involving search and rescue operations where they happen in the sea." 
 
 Malaysia Airlines' Mr. Ahmad said Zaharie Ahmad Shah, the 53-year-old captain of the missing plane, had 18,365 hours of experience and joined the airline in 1981. His 27-year-old deputy has more than 2,700 hours of flying experience. 
 
 Malaysian Airlines officials said in a press conference there is still no sign of wreckage from flight MH370, which disappeared from radar early on Saturday morning. They also said they are not hiding any information about the search efforts. (Photo/Video: AP) 
 
 Malaysia Airlines hasn't had any fatal accidents for the better part of two decades. In September 1995, a Malaysia Airlines Fokker 50 crashed in Tawau, Sabah, killing 34. The deadliest incident involving the airline was a December 1977 crash of a Boeing 737-200 jet in southern Johor state after an apparent hijacking attempt, killing all 100 on board. 
 
 Malaysia Airlines took delivery of its first 777-200 in 1997 and is evaluating new Boeing Co. and Airbus Group jetliners to replace the aging 777s in its fleet with newer, more-efficient models. 
 
 A Boeing spokeswoman said the company is "closely monitoring reports on Malaysia Flight MH370. Our thoughts and prayers are with everyone on board." 
 
 The 777 is among the most reliable of the current generation of widebody jetliners and years ago it pioneered extended overwater routes across the Pacific. 
 
 Boeing officials emphasize the 777's excellent safety features by pointing out that in millions of takeoffs, there hasn't been a single instance of an engine failing at the instant of liftoff from a runway. 
 
 —James T. Areddy, Newley Purnell, Sarah Sloat, Giovanni Legorano, Andy Pasztor, Jon Ostrower and Jeremy Page contributed to this article. 
 
 Write to Vu Trong Khanh at trong-khanh.vu@wsj.com, Gaurav Raghuvanshi at gaurav.raghuvanshi@wsj.com, Jason Ng at jason.ng@wsj.com and Celine Fernandez at Celine.Fernandez@wsj.com ||||| MILAN (AP) — Foreign ministry officials in Rome and Vienna confirmed Saturday that names of two nationals listed on the manifest of the missing Malaysia Airlines flight match passports reported stolen in Thailand. 
 
 A family member of passengers aboard a missing Malaysia Airlines plane is mobbed by journalists at Kuala Lumpur International Airport in Sepang, outside Kuala Lumpur, Malaysia, Saturday, March 8, 2014.... (Associated Press) 
 
 A spokesperson, right, from the Malaysia Airlines speaks to the media during a news conference at a hotel in Beijing Saturday, March 8, 2014. Search teams across Southeast Asia scrambled on Saturday to... (Associated Press) 
 
 A woman wipes her tears after walking out of the reception center and holding area for family and friend of passengers aboard a missing Malaysia Airlines plane, at Kuala Lumpur International Airport in... (Associated Press) 
 
 Neither European was on the plane, which disappeared Saturday less than an hour after it took off from Kuala Lumpur bound for Beijing, officials said. The Italian was traveling in Thailand and the Austrian was located in his native country. 
 
 The father of the Italian man told The Associated Press that his son's passport had been stolen a year and a half ago while traveling in Thailand. 
 
 "He deposited it with rental car agency, and when he returned the car it was gone," Walter Maraldi said by telephone from his home in the northern Emilia-Romagna region. 
 
 Walter Maraldi said authorities could not tell him whether the stolen passport or a counterfeit copy was used by a passenger to board the aircraft. 
 
 The father said his son Luigi Maraldi, 37, called his parents from Thailand to tell them he was fine after hearing news reports that an Italian with his name was on board the missing airplane. 
 
 Austrian Foreign Ministry spokesman Martin Weiss confirmed that a name listed on the manifest matches an Austrian passport reported stolen two years ago in Thailand. Weiss would not confirm the Austrian traveler's identity. 
 
 "We have no information on who might have stolen the passport," Weiss said. 
 
 ____ 
 
 AP reporter Frank Jordans in Berlin contributed to this report. ||||| Breaking News Emails Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings. 
 
 / Updated 
 
 Military radar suggests the missing Boeing 777 jet may have turned back before disappearing over the South China Sea, Malaysia's air force chief said Sunday. 
 
 Rodzali Daud told a press conference that "there is a possible indication that the aircraft made a turnback," adding that authorities were "trying to make sense of that." 
 
 Investigators were also checking surveillance footage of two passengers they believe boarded the Malaysia Airlines jet using stolen passports. Two names on the passenger manifest of the plane matched passports reported stolen in Thailand, one belonging to an Italian and the other to an Austrian. The passports' legitimate owners were not on the aircraft. 
 
 U.S. officials told NBC News on Saturday they were investigating terrorism concerns after the red-eye flight from Kuala Lumpur, Malaysia, to Beijing vanished in relatively clear weather, without sending a distress signal, at what analysts said would have been cruising altitude. 
 
 “We are aware of the reporting on the two stolen passports,�” one senior U.S. official said. “We have not determined a nexus to terrorism yet, although it’s still very early, and that’s by no means definitive.” 
 
 Officials note that there were other criminal reasons, such as drug smuggling, that stolen passports might be used to board a plane. 
 
 The Italian on the passenger list whose passport had been stolen was Luigi Maraldi, 37. His father, Walter Maraldi, told NBC News on Saturday that Luigi was vacationing in Thailand and had called to check in. 
 
 “We didn’t know about the accident,” the father said from Cesena, Italy. “Thank God he heard about it before us.” 
 
 Walter Maraldi said his son had his passport stolen a year ago in Thailand. 
 
 In Austria, the foreign ministry confirmed to NBC News that police had made contact with a citizen who was also on the passenger list, and who reported his passport stolen two years ago. 
 
 “We believe that the name and passport were used by an unidentified person to board the plane,” a spokesman for the ministry said. 
 
 It is unusual, but not unheard of, for one person to board a plane with a stolen passport. It is very rare for two people with stolen passports to board the same plane, terrorism analysts say. 
 
 International police body Interpol maintains a database of more than 39 million travel documents reported lost or stolen by 166 countries, and says on its website that this enables police, immigration or border control officers to check the validity of a suspect document within seconds. 
 
 "As far as we're aware, every one of the people onboard that aircraft had a visa to go to China. Which means those passports were in the possession of the Chinese Embassy before those visas were issued," Malaysia Airlines' director of commercial operations Hugh Dunleavy said. 
 
 Malaysia's transport minister Hishammuddin Hussein said that at least four names on the passenger list were under investigation, but that authorities would also focus on the entire passenger manifest. 
 
 He said help was also being sought from the FBI. 
 
 "We are looking at all possibilities," he added. "We cannot jump the gun. Our focus now is to find the plane." 
 
 A Malaysian official with knowledge of the investigation told Reuters the passengers being checked had bought their tickets through China Southern Airlines, which was code-sharing the flight with Malaysia Airlines. 
 
 According to Malaysia's civil aviation chief Azharuddin Abdul Rahman, five passengers booked on the flight did not board, and their luggage was removed. 
 
 Search operations continued Sunday for the missing jet, but officials said no sightings of the wreckage had been reported after an all-night search. Authorities confirmed an oil slick had been spotted by in the water off Vietnam. 
 
 The U.S. National Transportation Safety Board said it had dispatched a team to help investigate the crash. The NTSB team is accompanied by technical advisers from the Federal Aviation Administration and Boeing, which made the 777-200ER jet. 
 
 The aircraft was carrying 227 passengers and 12 crew. Most of the passengers were Chinese. Three were Americans — one adult and two children, according to the passenger manifest. 
 
 In Beijing, anguished families gathered at the airport and were taken to a hotel to wait for what little information there was. 
 
 The airline asked for prayers from the world. 
 
 The investigation is expected to be lengthy, partly because authorities would have to find wreckage and perform forensic tests. It took more than a year to rule out terrorism after the 1996 crash of TWA Flight 800 off Long Island. 
 
 When Air France Flight 447 went down in the Atlantic Ocean in June 2009, bodies and some parts of the plane were found within two weeks, but it took two years to find the main wreckage. 
 
 While flight data recorders and cockpit voice recorders, the so-called black boxes, can emit signals from underwater, it can be extremely difficult to find planes that disappear over the sea. 
 
 The last fatal crash for Malaysia Airlines was in 1995, when 34 people were killed near the city of Tawau. In 1977, a domestic Malaysia Airlines flight was hijacked and crashed, killing 100 people. 
 
 Andy Eckardt, Claudio Lavanga, Erin McClam, Jason Cumming, F. Brinley Bruton, Becky Bratu and Michele Neubert of NBC News contributed to this report. Reuters and The Associated Press also contributed.
– Night has fallen with search crews finding no wreckage from the Malaysia Airlines jet that is presumed to have crashed into the Gulf of Thailand south of Vietnam. The only clue remains two long streaks of oil in the water. The Boeing 777 had reported no problems before disappearing from radar, and authorities are nowhere near ready to speculate on what might have gone wrong. But most coverage is now taking note of one suspicious-seeming fact: Two of the passengers appeared to be traveling with stolen passports, reports the New York Times. Specifically, an Austrian and an Italian listed on the manifest had their passports stolen previously in Thailand, reports AP. Which may not mean anything, of course, and the Wall Street Journal quotes a European security official as saying it's not that unusual for stolen passports to turn up. But it's fishy enough to catch the attention of US security officials. “We are aware of the reporting on the two stolen passports,” one tells NBC News. “We have not determined a nexus to terrorism yet, although it’s still very early, and that’s by no means definitive.” The chief executive of Malaysia Airlines also addressed the reports, declaring that "we are not ruling out anything."