Investigators are examining surveillance footage of two passengers who boarded the missing Malaysia Airlines jet using stolen passports.
Azharuddin Abdul Rahman, the head of Malaysia's department of civil aviation, said officials had obtained video of the pair.
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. However, the passports' legitimate owners were not on board the flight.
U.S. officials told NBC News on Saturday they were investigating terrorism concerns after the Boeing 777 vanished over the South China Sea.
“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.”