Malaysian PM: Debris Found on Island Is from Flight 370

Yet authorities in France, the US and Australia were more cautious, stopping short of full confirmation. Some relatives said the mixed messages were causing them yet more confusion and anxiety.

The disappearance of the Boeing 777 jetliner 515 days ago while on a flight from Kuala Lumpur to Beijing on March 8, 2014, has been one of the biggest mysteries in aviation history. Officials believed it crashed in the southern Indian Ocean, killing all 239 people aboard, but it is unknown why the plane went down.

"It is with a very heavy heart that I must tell you that an international team of experts has conclusively confirmed that the aircraft debris found on Reunion Island is indeed MH370," Prime Minister Najib Razak told reporters. The French territory is thousands of miles from the area being searched for wreckage from the flight.

US and French officials involved in the investigation were more cautious, stopping short of full confirmation but saying it made sense that the metal piece of the wing, known as the flaperon, came from Flight 370, AFP reported.

The Australian government, which leads the seabed search for wreckage west of Australia, was also less certain than Malaysia, saying in a statement that "based on high probability, it is MH370."

Australia, which has sent an official to France to help examine the flaperon, has said the find will not affect its sonar search of a 120,000-square-kilometer (46,000-square-mile) expanse of seabed more than 4,000 kilometers (2,500 miles) east of Reunion Island.

That search, which began in October, has covered almost half that area without finding any clues.

"The fact that this wreckage does now look very much like it is from MH370 does seem to confirm that it went down in the Indian Ocean, it does seem very consistent with the search pattern that we've been using for the last few months," Australian Prime Minister Tony Abbott told Melbourne Radio 3AW. "Let's hope we can turn something up."

Intact and encrusted with barnacles, the flaperon was found on a beach and sent to France for scrutiny by the French civil aviation investigation department known by its acronym BEA, and members from its Malaysian and Australian counterparts.

"We now have physical evidence that, as I announced on 24th March last year, flight MH370 tragically ended in the southern Indian Ocean," Najib said.

"The burden and uncertainty faced by the families during this time has been unspeakable. It is my hope that this confirmation, however tragic and painful, will at least bring certainty to the families and loved ones of the 239 people onboard MH370," he said.

At a news conference in Paris, Deputy Prosecutor Serge Mackowiak didn't outright confirm that the debris belonged to Flight 370 but said there were strong indications that it was the case.

"The very strong conjectures are to be confirmed by complementary analysis that will begin tomorrow morning," Mackowiak said. "The experts are conducting their work as fast as they can in order to give complete and reliable information as quickly as possible."

Sara Weeks, the sister of New Zealander Paul Weeks who was on Flight 370, criticized the mixed messages on whether the flaperon had indeed been confirmed as part of the missing plane.

"It's somewhat frustrating," she said from Christchurch, New Zealand, where she lives.

"Why the hell do you have one confirm and one not? Why not wait and get everybody on the same page so the families don't need to go through this turmoil?" Weeks said.

Publicly, Australian officials withheld criticism of Najib's announcement, with Australian Transport Minister Warren Truss saying Malaysia, as the government in charge of the investigation, had the right to make that call.

"We respect the view that they believe they have sufficient evidence to make a categorical statement of that nature," Truss told reporters. "The French inquiry, of course, has not been quite so conclusive."

Privately, however, there were questions about why Najib had moved forward with the statement before all officials had agreed. An Australian government official, speaking on condition of anonymity because he wasn't authorized to speak publicly, said Malaysia wasn't supposed to make the announcement, and had gone out on its own making a conclusive statement before getting the evidence to back it up.

A US official familiar with the investigation said the flaperon clearly is from a Boeing 777. However, a team of experts in France examining the part hadn't yet been able to find anything linking it specifically to the missing plane, the official said, speaking on condition of anonymity because there was no authorization to talk publicly about the case.

With no other 777s or flaperons known to be missing, it makes sense that the part comes from Flight 370, but the US and Boeing team members are merely trying "to be precise," the official said.

Analysts say the investigators will examine the metal with high-powered microscopes to gain insight into what caused the plane to go down. It is also not known why Flight 370 - less than an hour into the journey - turned back from its original flight path and headed in an opposite direction before turning left and flying south over the Indian Ocean for hours.

Malaysia Airlines said in a statement that relatives of the passengers and crew "have already been informed and we extend our deepest sympathies to those affected."

The statement said the finding was "indeed a major breakthrough for us in resolving the disappearance of MH370. We expect and hope that there would be more objects to be found which would be able to help resolve this mystery."

Jacquita Gomes, the wife of crew member Patrick Gomes, said she was informed by the airline of the news about a half-hour before Najib's announcement.

"Now that they have confirmed it as MH370, I know my husband is no longer of this world but they just can't leave it with this one flaperon. We urge them to continue searching until they find the plane and bring it back," she said.

Highly technical efforts to extrapolate the jet's final hours before it would have run out of fuel gave force to the theory that it went down somewhere in the southern Indian Ocean.

No one is certain why the plane deviated so far from its planned route.

Analysts have said a close look at the wing part could indicate what kind of stress the plane was under as it made impact. It won't fully solve the mystery of why the plane disappeared, nor will it help pinpoint where the plane crashed.

A six-week air and sea search covering 4.6 million square kilometers (1.8 million square miles) of the southern Indian Ocean surface early last year failed to find any trace of the jetliner. The Reunion Island debris would be consistent with the working theory that the jet went down in the Indian Ocean and the debris was carried by the current, which moves counterclockwise.

Malaysian officials have said the plane's movements were consistent with deliberate actions by someone on the plane, suggesting someone in the cockpit intentionally flew the aircraft off course.

Since last year, Australian officials who are leading the search effort have operated on the theory that the plane flew on autopilot for hours before running out of fuel and crashing into the ocean. Investigators settled on that scenario after analyzing data exchanged between the plane and a satellite, which showed the jetliner took a straight path across the ocean.

In defining the search area, the Australian Transport Safety Bureau also operated on the theory that the crew was unresponsive, possibly suffering from oxygen deprivation, as the plane flew on autopilot. The agency said this was indicated by the loss of radio communications and a long period without any maneuvering of the plane, though it emphasized this was only a working theory and did not mean that accident investigators led by Malaysia would reach a similar conclusion.

A loss of cabin air pressure could cause oxygen deprivation, or hypoxia, which could make pilots unable to perform even basic tasks.