Vietnamese search planes spotted oil slicks near where a Malaysia Airlines jet carrying 239 people abruptly vanished on Saturday as it emerged that two passengers appeared to have been using stolen EU passports. Rescuers are still hunting for the whereabouts of the twin-engine plane going from Kuala Lumpur to Beijing more than 24 hours after it slipped off radar screens somewhere between Malaysia's east coast and southern Vietnam, triggering an international search effort. In a sign of the growing gloom over the fate of the aircraft, the airline early Sunday urged "all Malaysians and people around the world to pray for flight MH370". Air search operations were halted at nightfall, though ships continued searching, Malaysia Airlines said. The airline admitted: "It has been more than 24 hours since we last heard from MH370 at 1:30 am. The search and rescue team is yet to determine the whereabouts of the Boeing 777-200 aircraft." Adding to the mystery over the sudden loss of communication with the aircraft, it emerged that two people on the flight appeared to have been travelling on stolen EU passports. An Austrian, named in reports as Christian Kozel, had his passport pinched in Thailand in 2012, while Italian Luigi Maraldi, 37, had his stolen last year, also in Thailand, officials and sources said. Despite their names being on the passenger manifest, neither man was on the flight to Beijing. Martin Weiss, a spokesman for the Austrian foreign ministry, told AFP Kozel was "safe and sound" in Austria, but declined to comment on whether Vienna had been contacted by intelligence services for more information. Speaking to reporters in Malaysia, Deputy Transport Minister Datuk Aziz Kaprawi said authorities were probing the matter for possible foul play. "The information is still under review," he was quoted as saying by the Malay Mail Online. - 'All possibilities' being studied - In Washington, a US administration official said authorities were aware of the reporting of the two stolen passports. "We have not determined a nexus to terrorism yet, although it's still very early and that's by no means definitive. We're still tracking the situation," the official said. Earlier, when asked whether terrorism could have been a factor, Malaysian Prime Minister Najib Razak said: "We are looking at all possibilities but it is too soon to speculate." The plane was carrying 227 passengers -- including 153 Chinese nationals -- and 12 crew. Vietnam's military said two oil slicks had been spotted, but no debris. "Two of our aircraft sighted two oil slicks around 15 to 20 kilometres (10-12 miles) long, running parallel, around 500 metres apart from each other," the Vietnam army's deputy chief-of-staff, Vo Van Tuan, told state-run VTV. "We are not certain where these two oil slicks may have come from so we have sent Vietnamese ships to the area." "I think the two oil slicks are very likely linked to the missing plane," Vice-Admiral Ngo Van Phat, who is helping to direct the search mission, told AFP. - No distress signal - Flight MH370 had relayed no distress signal, indications of rough weather, or other signs of trouble, and both Malaysia's national carrier and the Boeing 777-200 model used on the route are known for their solid safety records. The plane's disappearance triggered a search effort involving vessels from several nations with rival maritime claims in the tense South China Sea. China, Vietnam, Malaysia, the Philippines and Singapore threw vessels and aircraft into the effort. Two Chinese warships were on their way to the possible crash zone, the Xinhua news agency said, quoting Chinese navy sources. The United States also dispatched a naval destroyer, with two helicopters aboard, and a surveillance plane. The South China Sea -- a vital shipping lane and a resource-rich area -- is the subject of overlapping claims and a growing source of friction between China and its neighbours. Contact with the aircraft was lost at around 1:30am Malaysian time (1730 GMT Friday), Malaysian authorities said, about an hour after take-off from Kuala Lumpur International Airport. Initially, authorities had put the last contact time at 2:40 am. The new time suggests the jet disappeared closer to Malaysia than first thought. If the worst is confirmed, it would be the second fatal crash ever for the widely used Boeing 777. A 777-200 operated by South Korea's Asiana Airlines skidded off the runway in San Francisco last year, killing three people. Malaysia Airlines has suffered few safety incidents in the past. Its worst occurred in 1977, when 100 people perished in a hijacking and subsequent crash in southern Malaysia. The 153 Chinese passengers aboard the plane included an infant, while 38 Malaysians and seven Indonesians were aboard. Six Australians, five Indians, four French nationals, and three Americans including an infant, were also among those listed and the Dutch Foreign Ministry said it believed one Dutch passenger was on the plane. The pilot had flown for the carrier since 1981, Malaysia Airlines said. The plane was more than 11 years old. The lack of information sparked fury among pained relatives in Beijing. "They should have told us something before now," a visibly distressed man in his 30s said at a hotel where passengers' families were asked to gather. Malaysia Airlines has sent a team of 93 people to China, whose tasks include helping distraught relatives. A deadly accident would be a huge blow for Malaysia Airlines, which has bled money for years as its struggles to fend off competition from rivals such as fast-growing Malaysia-based AirAsia.