Investigators searching for the missing Malaysian Airlines jet say terrorism is one line of inquiry.
Four suspect passengers who may have been travelling on false passports are under scrutiny.
The FBI is now helping investigators look into what happened.
The Boeing 777 disappeared from radar screens on Friday night - two hours into the flight from Kuala Lumpur to Beijing.
239 people were on board - the majority of whom were Chinese.
Malaysia's transport minister says there's a possibility the plane may have tried to turn back.
The Vietnamese Air Force has seen two oil slicks in the South China Sea, close to where it went missing, but no wreckage has been found.
Ignatius Ong, from the airline, says authorities in Malaysia, Singapore, Vietnam, and China are working together:
