The senior military official, who was not identified, told the U.S. news broadcaster the Boeing 777-200 that disappeared Saturday was far off course and heading back toward Malaysia -- instead of China -- when the plane's transponder, which gives its location, stopped.
"This kind of deviation in course is simply inexplicable," aviation expert Paul Goetz, former managing director of the National Transportation Safety Board, told CNN.
The Malaysian air force official indicated contact with the plane was lost over Pulau Perak, a small island in the Straits of Malacca -- hundreds of miles from the flight's normal path from Kuala Lumpur to Beijing. Most of the 239 people aboard were Chinese.
Earlier Tuesday, the head of Interpol in Lyon, France, said the disappearance of Flight MH370 does not appear to be terrorism-related.
One of two passengers traveling on a stolen passport aboard the missing Malaysia Airlines plane is an Iranian bound for Germany, but Malaysian officials said Tuesday the 18-year-old hasn't been linked to any terrorist activities, Inter-Asian News Service reported.
"The more information we get, the more we're inclined to conclude that it was not a terrorist incident," Interpol Secretary-General Ronald Noble said during press conference.
Noble said Malaysian authorities reported the Iranian teen, one of two people traveling on stolen passports aboard the missing airline, was trying to travel to his mother in Germany, CNN reported.
The plane, with 227 passengers and 12 crew members, vanished about an hour after departing Kuala Lumpur, Malaysia, Saturday.
Noble identified the pair as Pouri Nourmohammadi, 18; and Delavar Syed Mohammad Reza, 29. Malaysian authorities identified Nourmohammadi, with a slightly different spelling and age, and hadn't identified the second person.
The two passengers in question entered Malaysia using valid Iranian passports, Noble said. But they used stolen Austrian and Italian passports to board the missing plane, he said.
Malaysian Inspector-General of Police Khalid Abu Bakar was quoted in the Malaysian Star saying Nourmohammadi's mother contacted authorities when he failed to arrive in Frankfort, Germany.
"She was aware he was using a stolen passport," he said.
Malaysia Airlines Tuesday dismissed reports that five people checked in but did not board Flight MH370, clarifying that four people were not at the airport to check in for the flight, but had booked travel on the flight, Bernama reported.
Inspector-General of Police Tan Sri Khalid Abu Bakar also denied five people failed to board, saying all passengers who checked in had boarded.
Berita Harian reported a Singaporean air traffic control unit and the Royal Malaysian air force base in Butterworth reported receiving a signal the missing airliner turned back in South China Sea airspace on Saturday, the Malaysian Insider said.
Berita Harian quoted air force Gen. Tan Sri Rodzali Daud as saying the signal received indicated the plane was following its original route before it entered the airspace.