KUALA LUMPUR, Malaysia (AP) -- International intelligence agencies joined the investigation Sunday into two passengers who boarded the missing Boeing 777 jetliner with stolen passports, as Malaysian authorities said radar images showed the plane may have turned back before vanishing.
More than a day and half after Malaysia Airlines Flight MH370 went missing, no debris from the plane had been found, and the final minutes before it disappeared remained a mystery. The plane, which was carrying 239 people, lost contact with ground controllers somewhere between Malaysia and Vietnam after leaving Kuala Lumpur early Saturday morning for Beijing.
A massive international sea search has so far turned up no trace of the jet, though Vietnamese authorities said late Sunday that a low-flying plane had spotted a rectangular object in waters about 90 kilometers (56 miles) south of Tho Chu island, in the same area where oil slicks were spotted Saturday. State media speculated the object might be from the missing plane.
The missing plane apparently fell from the sky at cruising altitude in fine weather, and the pilots were either unable or had no time to send a distress signal - unusual circumstances under which a modern jetliner operated by a professional airline would crash.
Malaysia's air force chief, Rodzali Daud, said radar indicated that the plane may have turned back, but did not give further details on which direction it went or how far it veered off course.
"We are trying to make sense of this," Daud said at a news conference. "The military radar indicated that the aircraft may have made a turn back, and in some parts this was corroborated by civilian radar."
Malaysia Airlines Chief Executive Ahmad Jauhari Yahya said pilots are supposed to inform the airline and traffic control authorities if the plane does a U-turn. "From what we have, there was no such distress signal or distress call per se, so we are equally puzzled," he said.
Authorities were checking on the identities of the two passengers who boarded the plane with stolen passports. On Saturday, the foreign ministries in Italy and Austria said the names of two citizens listed on the flight's manifest matched the names on two passports reported stolen in Thailand.
"I can confirm that we have the visuals of these two people on CCTV," Malaysian Transport Minister Hishammuddin Hussein said at a news conference late Sunday, adding that the footage was being examined. "We have intelligence agencies, both local and international, on board."
Hishammuddin declined to give further details, saying it may jeopardize the investigation.
"Our focus now is to find the aircraft," he said, adding that finding the plane would make it easier for authorities to investigate any possible foul play.
White House Deputy National Security Adviser Tony Blinken said the U.S. was looking into the stolen passports, but that investigators had reached no conclusions.
In addition to the plane's sudden disappearance, which experts say is consistent with a possible onboard explosion, the stolen passports have strengthened concerns about terrorism as a possible cause. Al-Qaida militants have used similar tactics to try and disguise their identities.
Still, other possible causes would seem just as likely at this stage, including a catastrophic failure of the plane's engines, extreme turbulence, or pilot error or even suicide. Establishing what happened with any certainty will need data from flight recorders and a detailed examination of any debris, something that will take months if not years.
European authorities on Saturday confirmed the names and nationalities of the two stolen passports: One was an Italian-issued document bearing the name Luigi Maraldi, the other Austrian under the name Christian Kozel. Police in Thailand said Maraldi's passport was stolen on the island of Phuket last July.
A telephone operator on a China-based KLM hotline on Sunday confirmed that "Maraldi" and "Kozel" were both booked to leave Beijing on a KLM flight to Amsterdam on March 8. Maraldi was then to fly to Copenhagen, Denmark, on KLM on March 8, and Kozel to Frankfurt, Germany, on March 8.
She said since the pair booked the tickets through China Southern Airlines, she had no information on where they bought them.
Having onward reservations to Europe from Beijing would have meant the pair, as holders of EU passports, would not have needed visas for China.
Meanwhile, the multinational search for the missing plane was continuing. A total of 34 aircraft and 40 ships have been deployed to the area by Malaysia, Thailand, Australia, Singapore, Indonesia, China and the United States, in addition to Vietnam's fleet.