Vietnamese searchers say they looked through the night but have not found possible aircraft debris that was spotted Sunday evening during the hunt for a Malaysian passenger jet that vanished with 239 people aboard.
Vietnamese officials said searchers in a low-flying plane on Sunday had spotted what appeared to be a door from the missing airliner in waters 90 kilometers south of Tho Chu Island, located off Vietnam's southwest coast.
However, officials said on Monday that six planes and seven ships searching for the object had found nothing.
Earlier Sunday, officials investigating the disappearance of the Malaysia Airlines flight said radar images show the missing jet may have inexplicably turned back before vanishing.
Malaysia's air force chief gave no further details on which direction the Boeing 777-200 flying from Kuala Lumpur to Beijing went or how far it veered off course before disappearing early Saturday.
He said military and civilian radar indicated the aircraft may have made a turn back.
Also Sunday, Thai police said they were investigating a "passport ring" as details emerged of bookings for the flight made in Thailand with stolen European passports.
Two Europeans - Christian Kozel, an Austrian, and Luigi Maraldi of Italy - were listed on the passenger manifest of flight MH370, but neither man boarded the plane.
Both had their passports stolen in Thailand during the past two years. Malaysia has launched a terror probe investigating the suspect passengers and the United States has sent in the FBI to assist.
Malaysian Transport Minister Hishammuddin Hussein said authorities are investigating the identities of two additional passengers who boarded the plane with suspicious papers.
Interpol said Sunday no country had checked the international police agency's database that held information about the stolen Austrian and Italian passports used to board the Malaysia Airlines flight.
The Malaysia Airlines flight disappeared from radar screens about an hour after taking off from Kuala Lumpur for Beijing in good weather. Most of the passengers were Chinese.
Air traffic controllers say they never received a distress calls before the jet disappeared.
The Boeing 777-200 is a very popular plane with an excellent safety record.
The most recent accident involving a Boeing 777 was the Asiana Airlines crash at San Francisco International Airport in July 2013. Three people were killed. Pilot error is suspected in that incident.