WASHINGTON, March 8 -- The United States officials are investigating terrorism concerns over the missing Malaysia Airlines plane after two people listed as passengers of the MH 370 flight were confirmed not on board, and their passports were reported stolen in Thailand, local media reported Saturday.

U.S. officials said they had found no clear link to terrorism, but they were checking into passenger manifests and going back through intelligence, according to NBC News.

"We are aware of the reporting on the two stolen passports," said one U.S. senior official quoted by NBC News. "We have not determined a nexus to terrorism yet, although it's still very early, and that's by no means definitive."

The Austrian Foreign Ministry confirmed to Xinhua on Saturday that the 61-year-old Austrian man, who was listed on the missing Malaysia Airlines plane, was currently not on board but lives in Austria and in good health.

The 61-year-old Austrian lost his passport in Thailand in 2012, said Austrian Foreign Ministry spokesman Martin Weiss, adding that obviously there are no Austrian citizens on board.

The father of the Italian man who was thought to be on the same missing plane, Luigi Maraldi, told Xinhua that his son had the passport stolen last August at a vehicle rental shop in Thailand.

Maraldi phoned to his father early Saturday morning, telling him that he was not on the missing plane but safely in Thailand.

The flight MH370, a Boeing 777-200, was carrying 12 crew members and 227 passengers on board, including 154 Chinese, when it lost contact with Subang Air Traffic Control early Saturday morning.

An international search and rescue mission has so far failed to find evidence of any wreckage of the missing Malaysia Airlines flight, more than 24 hours after it was last heard, Malaysia Airlines said in its latest media statement released on Sunday.