NBC News is reporting that the U.S. government is investigating a possible terrorism link to the apparent crash of a Malasyian airliner bound for Beijing from Kuala Lumpur. An Italian national and Austrian national who reported their passports stolen last summer were listed on the passenger manifest despite not being on board the flight.

Authorities point out that there are other reasons passports are stolen, including drug smuggling. Officials are currently going over the passenger manifest looking for anyone with ties to terror groups.

“We are aware of the reporting on the two stolen passports,” one senior official said. “We have not determined a nexus to terrorism yet, although it’s still very early, and that’s by no means definitive.”

Both passports were stolen in Thailand, sources told NBC News.

An Italian man who had his passport stolen a year ago was on the passenger manifest for the jet, but his father told NBC News on Saturday that he was safe and on vacation 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 while traveling in Asia.

“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 for one person to board a plane with a stolen passport and very rare for two to do it, terrorism analysts say.

The Italian on the passenger list was Luigi Maraldi, 37. His father, Walter Maraldi, told NBC News from Cesena, Italy: “Luigi called us early this morning to reassure us he was fine, but we didn’t know about the accident. Thank God he heard about it before us.”

Malaysia has not seen significant terrorist activity, and airport security there has tended to be exemplary.

Asked earlier whether terrorism was suspected in the disappearance of the jet, Malaysian Prime Minister Najib Razak said authorities were “looking at all possibilities,” The Associated Press reported.

Earlier in the day, U.S. officials told NBC News that “all we know is something quick and catastrophic” happened to the plane.

Just what happened to the aircraft and where it went down are both matters of speculation, but terrorism is a very real possibility as I’ll explain on the next page.