Malaysia has finally come out with some details on what basis the flaperon found washed ashore on Reunion Island last week was conclusively identified to be from the missing MH370 aircraft.

On 5 August, Malaysian Prime Minister Najib Razak confirmed that the flaperon "conclusively" belonged to the aircraft but did not reveal details.

Despite the confirmation, France stopped short of declaring that the flaperon was from the aircraft, saying only that there was a "very strong presumption" based on technical data supplied by both the manufacturer Boeing and Malaysia Airline.

Deputy Paris Prosecutor Serge Mackowiak did not give any indication whether experts had found any serial numbers or unique markets that would give a definite confirmation that the flaperon belonged to MH370.

BBC said that Mackowiak's statement indicated that he was "exercising legal caution".

Relatives of those on board the missing aircraft have been upset and angry over the mixed signals given by Malaysia and France over whether the flaperon was definitely part of the plane or not.

The Boeing 777 was flying from Kuala Lumpur to Beijing on 8 March 2014 when it disappeared from radar. It had 239 passengers and crew members on board. Efforts to locate the plane have not been successful so far.

Malaysian Transport Minister Liow Tiong Lai said that a maintenance record seal on the flaperon was conclusive proof that it was part of the MH370.

A Malaysian Airlines maintenance expert identified the seal, he said.

"The part matches their maintenance records. The colour and other details also confirm it's from MH370," he said.

The Malaysian investigation team in Toulouse where the flaperon is now being looked at, also agreed with the conclusion. The team of experts includes officials from the airlines and the Department of Civil Aviation, The Star reports.

He said other investigators involved in the probe are still continuing with the verification process and were conducting tests on the part, saying that he understood why the French team had been less categorical in their conclusions over the flaperon.

"We appreciate the support of the French authorities and respect that they have chosen to continue the investigation process," said Liow.

The minister also said he had been told that a seat and window materials from an aircraft have been found washed up on the island.

He said the fresh debris was being studied and it has yet to be confirmed whether they belong to MH370. "I can only ascertain that it's plane debris," he said.

Relatives in China still sceptical

Bao Lanfang (C), whose son, daughter-in-law and 3-year-old granddaughter are missing, outside Malaysia Airlines' Beijing office on 6 August 2015. Grieving family members outside the Malaysia Airlines Beijing office on Thursday demanded more information and visas to travel to Reunion Island. REUTERS/Jason Lee

BBC said that the lack of consistent message from the relevant authorities investigating the debris found on Reunion Island has angered family members who had gathered outside Malaysia Airline's office in Beijing.

"France is being cautious about it, but Malaysia is desperate to put an end to this case and run away from all responsibilities," said Dai Shuqin, the sister of one of the missing passengers.

"We suspect that the plane wreckage could be faked," said Liu Kun, whose younger brother was on board the plane.

Liow told reporters that Malaysia will be holding a joint meeting with China and Australia on the next steps in the search for the missing plane.

"I have called my counterpart in China, Yang Chuantang, and we are discussing a suitable date for the meeting," he said, adding that the search, which is in its second phase, will now continue until the beginning of 2016, according to the Star.