Passports stolen from an Italian and Austrian national and used by two passengers to board the missing Malaysian plane are now being investigated by United States officials for possible terrorism links.

US officials said they had found no clear link to terrorism so far, but they were checking into the passenger manifest and running all the names through intelligence, according to NBC News.

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The Interpol confirmed that the stolen Italian and Austrian passports were in its database, but no country ever inquired about them, it said. 

Italian Luigi Maraldi had alerted the Italian Foreign Ministry in August 2013 that his passport was stolen while he was vacationing in Asia. Austrian officials said Christian Kozel reported the loss of his passport in 2012 while he was also traveling in Asia.

Maraldi and Kozel said they were not on board Malaysia Airlines Flight MH370, but their names were found to have been ticketed to fly from Kuala Lumpur to Beijing, and on to Europe.

More than 48 hours after Flight MH370 vanished mid-flight on its way to Beijing from Kuala Lumpur, investigators and search and rescue teams are nowhere close to finding any traces of the plane nor clues to what actually happened.

Relatives of the passengers have grown increasingly weary and angry over the long wait for clear information on the fate of the plane that was due to land in Beijing at 6:30am local time on Saturday, but never arrived.

Family and friends of the 154 Chinese passengers were brought to a hotel near Beijing airport where authorities tried to shield them from media.  By Sunday, some were undecided whether to stay on at the hotel or not.

"My son was only 40 years old," one woman wailed as she was led inside. "My son, my son. What am I going to do?"

"Has the plane not yet found?" asked one man in a soft, trembling voice. "All my family members are there. I am the only one in my family not on the plane," he said.

One angry relative almost smashed a reporter's camera.

Malaysia Airlines said they are coordinating with authorities to be able to fly the relatives to Kuala Lumpur and will shoulder all their travel costs. Two relatives of each passenger will be allowed to go.

The Chinese and Malaysian governments are working together to facilitate the issuance of travel papers to relatives who will be going to Malaysia. 

The first batch of relatives is expected to arrive in Kuala Lumpur in one to two days. The second and third batches will be brought to the point of last contact with the plane, once it is established that the plane indeed went down.