A piece of a wing found washed up on Reunion Island last week is from Malaysia Airlines Flight 370 that vanished last year, Malaysia's prime minister announced early Thursday, saying he hoped the news would end the "unspeakable" uncertainty of the passengers' families.

The disappearance of the Boeing 777 jetliner 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, mostly from China, but it is not ll 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.

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.

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 began in October and 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.

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, 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," he said. "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."