Malaysia's Prime Minister Najib Razak has confirmed that plane debris discovered on an island in the Indian Ocean is from missing flight MH370.
International crash experts have been examining the wing part found on the island of Reunion last week, hoping to determine whether it comes from the jetliner.
At a news conference, Mr Razak said the international team of experts had conclusively confirmed that it was from the Malaysian Airlines aircraft.
He said his government was committed to finding the truth of what happened to the plane, which disappeared in March 2014 with 239 people on board.
"Today, 515 days since the plane disappeared, 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 from MH370," Mr Najib told reporters.
"We now have physical evidence that, as I announced on 24th March last year, flight MH370 tragically ended in the southern Indian Ocean."
Very strong indications - French prosecutor
At a press conference in Paris, however, a French prosecutor was more cautious.
Serge Mackowiak confirmed the wing fragment, known as a flaperon, was from a Boeing 777 - the same make and model as the missing Malaysian airliner.
And he said initial tests showed there were "very strong indications" that it was from flight MH370. But he said confirmation would only come after further tests on the fragment, which would begin on Thursday.
"[Investigators] will try to do it as soon as possible in order to provide total and reliable information to the family of victims, who are on our minds at the moment," Mr Mackowiak said.
The BBC's Hugh Schofield said the Paris prosecutor was simply exercising "supreme legal caution".
There is little doubt he will also declare the flaperon the first evidence from MH370 in the coming days as no other Boeing 777s are thought to have crashed in the region.
Mr Mackowiak said a fragment of suitcase, also found on Reunion, would be subjected to forensic examination as soon as possible.
The flaperon is being analysed in Toulouse by experts in the presence of French, Malaysian, Chinese and American representatives. Officials from the manufacturer Boeing are also there.
Bertrand Vilmer, a veteran aeronautic specialist, said the experts would be looking for clues to explain how the wing part was damaged.
"They will look to see if there are any traces, any particular holes, any signs of an explosion, any traces of a fire, of an electrical fire, traces of compression, of a breakage, if the breakage was a due to a strain, to a shearing and so on," he told the BBC.
Reunion is roughly 3,700 km from the broad expanse of the southern Indian Ocean off Australia where search efforts have focused, but officials and experts said currents could have carried wreckage that way, thousands of kilometres from where the plane is thought to have crashed.
- Reuters, BBC