France said Thursday it would launch new searches by air, land and sea from Reunion in the hopes of finding more wreckage from MH370, after Malaysia said a wing part washed up on the Indian Ocean island came from the ill-fated flight.

A Casa military aircraft will begin surveying the area from Friday morning, the French government said in a statement. The search will also be stepped up with foot patrols, helicopters and maritime units, it added.

"Any discovery will be immediately made available to the investigation," said the joint statement by the French ministers of defence, transport and overseas territories.

Separately, local authorities for the island district where the first piece of debris was found said they would organise a thorough search for other parts from the plane starting Monday.

The renewed efforts to hunt for MH370 wreckage came after Malaysian Prime Minister Najib Razak announced that a two-metre-long (almost seven-foot) wing part that was discovered on French Reunion island last week was confirmed as coming from the missing aircraft, the first physical proof it met a tragic end in the Indian Ocean 17 months ago.

"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 said earlier Thursday.

But the announcement was not universally welcomed by the relatives of those on board, with some relatives of the 239 people on board expressing scepticism and voicing fresh criticism of officials' handling of the disaster.

The Malaysia Airlines Boeing 777 disappeared on March 8 last year, inexplicably veering off course en route from Kuala Lumpur to Beijing.

- 'Baffling mystery' -

The search for MH370 turned into one of the biggest mysteries in the history of aviation, sparking a colossal hunt in the Indian Ocean based on satellite data which hinted at MH370's possible path.

Malaysia Airlines described confirmation that the wing part came from MH370 as a "major breakthrough" that it said would hopefully help to find the plane somewhere in the depths of the Indian Ocean.

Australian authorities, who have led a multinational search for the aircraft, expressed confidence that they were searching in the right area and that the body of the plane would eventually be found.

"It suggests that for the first time we might be a little bit closer to solving this baffling mystery," Australian Prime Minister Tony Abbott said.

But French prosecutors involved in determining if the wing part was from MH370 used more cautious language than Najib, saying only there was a "very high probability" it came from the plane.

Malaysian Transport Minister Liow Tiong said on Thursday that more possible MH370 objects -- aircraft seat cushions and windows -- had been discovered on Reunion, but "it has to be verified by the French authorities".

A French judicial source however said French investigators had not received any new items.

- Anger, distrust -

Anguished family members have been waiting for news with a mix of anticipation and dread, and some said the first concrete proof of the plane's fate would help bring closure.

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," she told the Fairfax New Zealand media group.

But some relatives who have consistently criticised Malaysia's handling of the crisis, particularly in China where most of the passengers were from, refused to believe the wing part was from the plane.

They have accused Najib's government and the airline of a bungled response to the disaster, possible cover-up and insensitive treatment of families -- charges that have been vehemently denied.

Some continued to insist on Thursday they would not believe the Malaysian authorities until the plane's black box data and flight recorders were recovered, or bodies were found.

"Where is my husband's body? Have any passengers' belongings been found? No. It's just a piece that they found," said Elaine Chew, whose husband Tan Size Hiang was part of the cabin crew.

"No, this is not closure for me."

Zhang Yongli, whose daughter was on the plane, similarly voiced her anguish, anger and distrust.

"I don't believe this latest information about the plane, they have been lying to us from the beginning."

"I know my daughter is out there, but they won't tell us the truth," he added, waving Chinese and Communist Party flags.

Still, China's foreign ministry said Najib's declaration "confirmed the verdict on the Malaysia Airlines accident", and expressed "deep grief" for the passengers.

Gerry Soejatman, a Jakarta-based aviation consultant, said people had to be realistic in their expectations and that it was lucky "that we found something at all".

"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."

It is hoped that more detailed examination in the coming days may indicate how the piece detached from the wing and whether it showed traces of an explosion or fire.

Scientists have also said barnacles on the flaperon could indicate how long it was in the water, and perhaps where it had been.

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