What had been thought were possible clues to the disappearance of a Malaysian jetliner have turned out to be unconnected to the plane.
Malaysian maritime officials found some oil slicks in the South China Sea on Saturday, but after sending a sample to a lab, investigators announced Monday that the oil was not from an aircraft at all, according to The Associated Press.
Another sign of the missing aircraft, a yellow object floating in Vietnamese waters that rescue teams hoped was a life raft, turned out to be unrelated debris, the Civil Aviation Authority of Vietnam said, leaving rescuers to continue their search for any sign of the aircraft and its 239 passengers.
A searcher on a Vietnamese jet saw the object earlier Monday but was unable to get close enough to determine what it was, Pham Quy Tieu, vice transport minister and deputy head of the country's rescue committee, told Reuters.
The aviation authority said on its website that further searches were being conducted about 90 miles southwest of Tho Chu Island, off Vietnam's southern coast.
The sighting of the yellow object had been the first lead in the effort to determine what happened to Malaysia Airlines Flight MH370, which left Kuala Lumpur early Saturday for Beijing but never arrived. An unknown source said preliminary investigations are narrowing on the possibility of midair disintegration, Reuters reported.
On Sunday, Vietnamese searchers in a low-flying plane spotted an object that appeared to be one of the plane's doors on Sunday, the state-run Thanh Nien newspaper said, citing the deputy chief of staff of Vietnam's army, Lt. Gen. Vo Van Tuan.
Ships from the maritime police headed to the site, about 60 miles south of Tho Chu in the Gulf of Thailand. It is the same area where Vietnam said on Saturday that its rescue planes had spotted two large oil slicks, about 9 miles long, and a column of smoke off its coast.
But by Monday morning, after working through the night, Vietnamese searchers had not found the object thought to be a door.
On Sunday, Malaysia Airlines said it was "fearing the worst," and the government said it was investigating four passengers who may have held false identity documents.
There were no reports of bad weather and no signs why the Boeing 777-200ER would have fallen off radar screens about an hour after it took off from Kuala Lumpur for Beijing. The Malaysian military said the missing flight turned back before disappearing, according to a radar report.
"We are not ruling out any possibilities," Malaysia Airlines CEO Ahmad Jauhari Yahya told a news conference. The country's transport minister said Sunday the search area has been expanded because of a possibility the missing aircraft had turned back.
Malaysian investigators are checking the identities of four passengers on the missing flight but have not yet determined if the plane was downed by an attack, Defense Minister Hishamuddin Hussein said.
"All the four names are with me," he told reporters.
He confirmed that Malaysian investigators had met with their counterparts from the FBI and said the investigation was focusing on the entire passenger manifest. Interpol said it was of "great concern" passengers were able to board the international flight with passports registered in a lost or stolen database, which hadn't been consulted prior to boarding, Reuters reported. At least two stolen or lost passports were used to board the missing flight, Interpol added.
Malaysia's state news agency quoted Home Minister Ahmad Zahid Hamidi as saying the passengers using the stolen European passports were Asian in appearance and criticizing border officials who let them through.
"I am still perturbed. Can't these immigration officials think? Italian and Austrian (passport holders) but with Asian faces," he was quoted as saying late on Sunday.
However, both Reuters and AP have reported that the two passengers traveling with stolen passports were, in fact, not Asian-looking men, according to security videos.
The passenger manifest issued by the airline included the names of two Europeans who were not on the plane, according to their foreign ministries, because their passports had been lost or stolen.
A Foreign Ministry spokesman in Vienna said, "Our embassy got the information that there was an Austrian on board. That was the passenger list from Malaysia Airlines. Our system came back with a note that this is a stolen passport."
Austrian police found the man safe at home. The passport was stolen two years ago while he was traveling in Thailand, the spokesman said.
The Foreign Ministry in Rome said no Italian was on the plane either, despite the inclusion of Luigi Maraldi's name on the list. His mother, Renata Lucchi, told Reuters his passport was lost, presumed stolen, in Thailand in 2013.
U.S. and European security officials said that there was no proof of any terrorist link and there could be other explanations for the use of stolen passports.
The 11-year-old Boeing took off at 12:40 a.m. (12:40 p.m. ET) Friday from Kuala Lumpur International Airport and was apparently flying in good weather conditions when it went missing without a distress call.
Flight MH370 last had contact with air traffic controllers 120 nautical miles off the east coast of the Malaysian town of Kota Bharu. Flight tracking website FlightAware.com showed it flew northeast after takeoff, climbed to 35,000 feet and was still climbing when it vanished from tracking records.
A large number of planes and ships from several countries were scouring the area where the plane last made contact, about halfway between Malaysia and the southern tip of Vietnam.
Search and rescue vessels from the Malaysian maritime enforcement agency reached the area where the plane last made contact but saw no sign of wreckage, the Malaysian Maritime Enforcement Agency said.
China and the Philippines also sent ships to the region to help, and the United States, the Philippines and Singapore dispatched military planes. China put other ships and aircraft on standby.
Ross Aimer, a former pilot with United Airlines, told Al Jazeera it was highly unusual that air traffic control would lose contact with an aircraft without communication from the crew.
"The fact that there was absolutely no distress signal is very disturbing. This is almost unprecedented that we lose an aircraft in such a way ... In that area of the world, over Vietnam, there is sporadic radar coverage to begin with," he said.
Chinese Foreign Minister Wang Yi told reporters in Beijing that China was "extremely worried" about the fate of the plane and those on board. Chinese passengers' relatives angrily accused the airline of keeping them in the dark, and state media criticized the carrier's response as poor.
"There's no one from the company here. We can't find a single person. They've just shut us in this room and told us to wait," said one middle-aged man at a hotel near the Beijing airport, where the relatives were taken.
"We want someone to show their face. They haven't even given us the passenger list," he said. Another relative, trying to evade a throng of reporters, muttered, "They're treating us worse than dogs."
Malaysia Airlines said it deployed a team of caregivers and volunteers to assist the family members of the passengers in China. "Our sole priority now is to provide all assistance to the families of the passengers and our staff," according to a company statement.
The airline said people of 14 nationalities were among the 227 passengers, including at least 152 Chinese, 38 Malaysians, seven Indonesians, six Australians, five Indians, four French and three Americans.
In Kuala Lumpur, Malaysia Airlines told passengers' next of kin to go to the international airport with their passports to prepare to fly to the crash site once it was identified.
"Immediate families of passengers are advised to gather at Kuala Lumpur. Travel arrangements and expenses will be borne by Malaysia Airlines. Once the whereabouts of the aircraft (are) determined, Malaysia Airlines will fly members of the family to the location," the company said in a statement.
About two dozen families were being kept in a holding room at the airport, where they were being guarded by security officials and kept away from reporters.
Malaysia Airlines has one of the best safety records among full-service Asia-Pacific carriers.
Al Jazeera and wire services