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. What is certain is that “something very sudden happened”:

Malaysia Airlines Flight MH370 was en route from Kuala Lumpur to Beijing when it lost contact with air traffic controllers around 2:40 a.m. local time Saturday, two hours after takeoff, the airline said.

The airline’s chief executive, Ahmad Jauhari Yahya, told a news conference in Kuala Lumpur that there was no distress call or bad weather report from the pilots before the plane lost contact with air control 120 nautical miles (140 miles) off the east coast of Kota Bharu, Malaysia.

As the search-and-rescue effort got underway, in addition to Vietnamese aircraft, China sent two ships to assist, state-run CCTV reported, while Singapore dispatched a C-130 aircraft. Malaysia sent three maritime enforcement ships, a navy vessel and three helicopters, a Malaysian Maritime Enforcement Agency official told Reuters.

Mikael Robertsson, cofounder of FlightRadar24, which tracks about 120,000 flights per day with 3,000 receivers around the world, said the last transmission it recorded from the flight was at 35,000 feet. While it’s possible the plane veered into an area too far away from receivers to track it, he said that was unlikely.

“In this case, we have quite good coverage,” he said. “We had a very good stable signal and it just disappeared …. I don’t want to speculate, but something very sudden happened.” FlightRadar representatives also said they believed the plane had lost radar contact about 40 minutes into the flight, not two hours as the airline said.

The recent terror attack at a train stationin China’s Xinjiang province by Muslim terrorists that killed 29 and wounded more than one hundred people suggests that terrorism may very well be a possibility in the downing of the Malaysia Airlines jet. But it may be many weeks or months before investigators will be able to confirm exactly what happened to cause the 777 to drop out of the sky.