It's believed part of the missing Malaysia Airlines jet has been found off the coast of Vietnam.

Photos show what looks like a plane door in the sea.

Interpol says it's greatly concerned that at least two passengers on the flight - which vanished on Friday - were able to use stolen passports.

It's still not clear whether the plane was lost through a terrorist attack or because of an accident.

Former US department of transport inspector Mary Schiavo says the debris will be inspected for traces of explosive material.

May have turned back

Radar signals suggest the missing Malaysian Airlines plane may have turned back before vanishing.

An international search is under way for Flight 370, which was carrying 239 people when it disappeared on Friday.

Tracy Vo from Australia's Channel 9 says sightings of an oil slick yesterday didn't lead to anything.

Interpol Secretary General Ronald K. Noble said no checks were made on the two passports prior to the flight.

"If Malaysia Airways and all airlines worldwide were able to check the passport details of prospective passengers against INTERPOL's database, then we would not have to speculate whether stolen passports were used by terrorists to board MH 370.

"We would know that stolen passports were not used by any of the passengers to board that flight," he said.

Luigi Maraldi is the Italian man who's lost passport was used by someone to get onto the flight.

He didn't think it could be used after he reported it lost.

Air Traffic Control Consultant David Smillie says the answers to what happened will be in the plane's 'black box' and voice recorder:

Image: Marker on Tho Chu Island in Gulf of Thailand, near which debris has reportedly been found by search crews.