KUALA LUMPUR/BEIJING, March 9 -- Malaysian civil aviation authorities said Sunday that search operations continued overnight for the missing Malaysia Airlines jet but have so far failed to locate the Boeing 777 aircraft.

Officials from Malaysia's Department of Civil Aviation said at a press conference that they have also dispatched three planes to join the hunt for Flight MH370, which has lost contact with traffic control for more than 30 hours.

In its latest statement, Malaysia Airlines said "the search and rescue teams are still unable to detect the whereabouts of the missing aircraft," which was carrying 227 passengers and 12 crew members from Kuala Lumpur to Beijing.

The company said it will set up a command center at Kota Bharu, Malaysia, or Ho Chi Minh, Vietnam, as soon as the location of the aircraft is established.

"In fearing for the worst, a disaster recovery management specialist from Atlanta, USA, will be assisting Malaysia Airlines in this crucial time," added the airline.

Meanwhile, the United States was reportedly investigating terrorism concerns over the missing plane as two people listed as passengers of the MH370 flight were found not on board and their passports were reported stolen in Thailand.

U.S. officials told NBC News that they were "aware of the reporting on the two stolen passports" and have found no clear link to terrorism, but they were checking into passenger manifests and going back through intelligence.

A senior U.S. official was quoted as saying that "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 listed in the MH370 manifest was currently not on board but lives in Austria and in good health.

The Austrian lost his passport in Thailand in 2012, said Austrian Foreign Ministry spokesman Martin Weiss, adding that obviously there is no Austrian citizen on board.

Earlier that day, the father of Luigi Maraldi, the Italian man who was thought to be on the same missing plane, told Xinhua that his 37-year-old son had his passport stolen last August at a vehicle rental shop in Thailand.

Maraldi phoned his father early Saturday morning to tell him that he was not on the missing plane and safe in Thailand.

However, a Malaysia Airlines spokesman said the stolen passport incidents have not been confirmed by Malaysian authorities.

Asked whether the incident was a terrorist attack at a press conference Saturday, Malaysian Prime Minister Najib Razak said, "We are looking at all possibilities but it is too soon to speculate."

"The search and rescue operations will continue," Najib said, adding that the search area was expanded after international rescuers failed to locate the missing plane from its last point of contact.

Also on Saturday, Vietnamese Deputy Transport Minister Pham Quy Tieu said rescuers were expected to arrive at waters where two "suspicious" oil slicks were spotted.

With 154 Chinese on board, Chinese President Xi Jinping has ordered that all-out efforts be made to help search and rescue the missing aircraft. Chinese divers, salvagers and warships are already on their way to the sea area where the jet is suspected to have crashed.

In addition, Singapore, Thailand, the United States and Vietnam have also offered help for the hunt.