PARIS — A sea-crusted wing part washed up on an island in the western Indian Ocean may be the first trace of Malaysia Airlines Flight 370 since it vanished nearly a year and a half ago, and a tragic but finally solid clue to one of aviation’s most perplexing and expensive mysteries.

Malaysia’s prime minister said Thursday the debris found on the French island of Reunion will be sent for investigation to the French city of Toulouse, the center for European aviation.

“We have had many false alarms before, but for the sake of the families who have lost loved ones, and suffered such heartbreaking uncertainty, I pray that we will find out the truth so that they may have closure and peace,” Najib Razak said on his personal blog.

Najib promised to make any new information public quickly.

Air safety investigators — one of them a Boeing investigator — have identified the component as a “flaperon” from the trailing edge of a Boeing 777 wing, a U.S. official said. Flight 370, which disappeared March 8, 2014, with 239 people on board, is the only 777 known to be missing.

“It’s the first real evidence that there is a possibility that a part of the aircraft may have been found,” said Australian Transport Minister Warren Truss, whose country is leading the search for the plane in a remote patch of ocean far off Australia’s west coast. “It’s too early to make that judgment, but clearly we are treating this as a major lead.”

Flight 370 had been traveling from Kuala Lumpur to Beijing, but investigators believe based on satellite data that the plane turned south into the Indian Ocean after vanishing from radar. If the wing part is from the Malaysian plane, it would bolster that theory and put to rest others that it traveled north, or landed somewhere after being hijacked.

The wing piece is about 2 meters (6 feet) long. Investigators have found a number on the part, but it is not a serial or registration number, Truss said. It could be a maintenance number, which may help investigators figure out what plane it belongs to, he said.

A French official close to an investigation of the debris confirmed Wednesday that French law enforcement is on Reunion to examine it. A French television network was airing video from its Reunion affiliate of the debris. U.S. investigators are examining a photo of the debris.