The washed-up plane part that was found on the French Indian Ocean island of La Reunion. (AFP Photo)

Debris found on a remote island a week ago is from flight MH370, Malaysia's prime minister said Thursday, confirming that the plane which mysteriously disappeared 17 months ago met a tragic end in the Indian Ocean."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," Najib Razak told reporters.French prosecutors used more cautious language, saying only there was a "very high probability" the wreckage came from MH370.The Malaysia Airlines jet disappeared on March 8 last year, inexplicably veering off course en route from Kuala Lumpur to Beijing with 239 people on board.The disappearance created one of the biggest mysteries in the history of aviation, sparking a colossal, multinational hunt for the aircraft and a myriad of conspiracy theories about its fate.Last week's discovery of a two-metre-long (almost seven-foot) wing part called a flaperon on the French Indian Ocean island of La Reunion provided the first glimmer of hope for relatives desperate for answers.It was examined on Wednesday at a military lab outside the French city of Toulouse in the presence of Malaysian and Australian experts, Boeing employees and representatives from China -- the country that lost the most passengers in the disaster."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.Malaysia Airlines hailed the news as a "major breakthrough"."We expect and hope that there would be more objects to be found which would be able to help resolve this mystery," said the airline in a statement.Australian authorities, who have been leading the massive search for the plane, on Thursday also expressed optimism that the main part of the plane would be found."We're confident that we're looking in the right area and we'll find the aircraft there," Martin Dolan, chief commissioner of the Australian Transport Safety Bureau, told ABC radio.Sara Weeks, the sister of MH370 passenger Paul Weeks of New Zealand, said the confirmation ended "a week of turmoil"."We've had 17 months of nothing... so actually finding something is the first step towards pinpointing where it is," Weeks told the Fairfax New Zealand media group.Some families said the confirmation was not enough to lay the matter to rest, as they reiterated demands to know why the plane went off course, flying for hours after its communications and tracking systems were shut down."Now I want to know where the main body of the plane is so that we can take out the passengers and get the black box so we can know what happened. Only that, for us, will be full closure," said Jacquita Gonzales, wife of MH370 chief steward Patrick Gomes.Gerry Soejatman, a Jakarta-based aviation consultant, said proof the flaperon came from MH370 was a "huge step"."People want all the answers, but look, let's be real. We must be glad that we found something at all. Now we know roughly where it might have crashed," he said."This answers a lot of questions actually. It eliminates other theories, conspiracy theories. If the black box is found later on, it is likely we could get more answers."The discovery of the flaperon on La Reunion sparked a rush of beachcombers scouring the coast for more debris.But Australian authorities said Thursday that "so far none of it, under examination, has been confirmed as coming from an aircraft"."The drift modelling indicates that if there is any more floating debris from MH370, it could be anywhere in hundreds of thousands of square kilometres in the Indian Ocean," said a statement from Australia's Transport Safety Bureau (ATSB), which has been heading up the search.The Malaysian premier gave no indication that the analysis of the debris yielded any clues into the cause of the disappearance.Many relatives accuse his government and the airline of a bungled response to the disaster, possible cover-up, and insensitive treatment of families, charges that are vehemently denied."I would like to assure all those affected by this tragedy that the government of Malaysia is committed to do everything within our means to find out the truth of what happened," Najib said."MH370's disappearance marked us as a nation. We mourn with you, as a nation."It is hoped that more detailed examination in the coming days can yield information on the final moments of the plane by showing how the piece detached itself from the wing, or whether it showed traces of an explosion or fire.Scientists have also pointed to the barnacles attached to the flaperon, saying these could give an idea of how long the fragment had been in the water, and perhaps where it had been."If it has cold-water barnacles on it that might tell them it went down further south than they think. Or if it's got only tropical barnacles, that might tell them it went down further north," said Shane Ahyong, a crustacean specialist from the Australian Museum.Australian aviation expert Neil Hansford said the flaperon snapping off hinted that the aircraft had gone "into the water in a controlled-type crash".But he added that at this time "all you can say that it proves is that MH370 definitely crashed into the southern Indian Ocean and it also proves that the search area as identified by the Australian experts... is appropriate."