France has launched a renewed air and sea search around the Indian Ocean island of Réunion in the hope of finding more debris from the missing Malaysia Airlines flight MH370.

The operation was announced 24 hours after a public prosecutor declared there was a “strong possibility” a wing flaperon discovered on a beach on Réunion was from the Boeing 777 that disappeared in March 2014 with 239 people on board.

Jacques Luthaud, commander of the French armed forces in the region, said the search area off the east coast of the island measured 120km (75 miles) by 40km (25 miles).

Authorities on the island said that since the discovery of the flaperon nine days ago 90 pieces of debris had been sent for examination to determine whether they are fragments of aircraft or not.

The search comes amid deteriorating relations between France, which is now heading the international investigation into the crash, and Malaysian officials who have been accused of “misinformation” and headline seeking.

While Malaysian officials have stated the wing debris is definitely from flight MH370, French officials heading a legal investigation have been considerably more cautious.

In Beijing, Chinese relatives of missing MH370 passengers marched to the Malaysian embassy to show their frustration with the search progress. Some demanded to be taken to Réunion island to see the suspected debris for themselves.

MH370 map

The announcement of a renewed search was made in a joint statement from France’s overseas and transport ministries. “Complementary analyses on this piece [flaperon] are being currently carried out. Following a request from the president and the prime minister, and to meet the needs of the inquiry, we have decided to deploy additional air and sea resources to establish the possible presence of new debris off Réunion,” it said.

On Friday morning, islanders reported a Casa plane overflying the zone around the Saint André beach where the flaperon was discovered. French soldiers have also been deployed to comb the beaches and coastline, along with gendarmes and helicopters.

“France is fully playing its role in this international operation by making available all necessary means to help throw light on this tragedy,” added the ministerial statement, concluding: “The French government understands the pain of the families for whom the discovery (of the flaperon) has awakened the hope of discovering the circumstances of flight MH370’s disappearance.”

The mayor of Saint-André also announced an inch-by-inch search of the coastline from Monday and said any passengers’ families who wished to travel to the island would be welcomed by locals.

The French state’s representative in Réunion, Dominique Sorain, told a press conference on Friday: “We are looking for other debris on the beaches. This is what the government has asked me to do.

“We will be searching on the coastline and around the east of Réunion, according to calculations of sea currents, right up to the sea limit of Mauritius. If necessary, marine patrols can be mobilised.”

Sorain said cargo ships in the Indian Ocean would be asked to keep a lookout for debris. All debris already collected has been sent for analysis, he added, but it was not possible at the current time to say if it came from flight MH370.

Sorain reiterated the Paris deputy prosecutor’s line that there was a “strong possibility” that the wing flaperon found last week was from the missing aircraft.

Sorain added that there was cooperation with the authorities and civil airlines on Mauritius.

“Nobody could have imagined that a piece of debris would have washed up on a beach in Reunion. It’s impossible to say if we will find any more debris, but we have to verify across the island.”

There is growing unease in France – and among the families of MH370 passengers – over a statement from Kuala Lumpur. On Thursday, the Malaysian transport minister Liow Tiong Lai claimed seat cushions and a window had been found on Réunion and handed over to French investigators, who later denied they had received any new debris.

However, Christophe Naudin, a French air safety specialist, told L’Express magazine the language of the announcements – that of the Malaysian prime minister and the Paris public prosecutor – might have been different but they were saying the same thing.

“The Boeing technicians confirmed that it (the flaperon) was a piece of a 777 and no other aircraft of this type is reported missing. The Malaysia Airlines experts then noted elements that linked it with MH370. No airline could have lost this kind of piece (of aircraft) without reporting it, so that leaves one possibility,” Naudin said.

He said the prosecutor’s office was showing an “excessive administrative precaution which revealed an ignorance of the aeronautic business”.

The Paris public prosecutor’s office has denied any errors in its communications.

“We have to talk within a judicial framework which means we have to be rigorous, complete and reliable. We will speak with certainty when the experts do so. There are still tests to be carried out,” a legal source told the magazine.

Frenchman Ghyslain Wattrelos, 50, whose wife and two children were travelling on MH370, which veered off route and disappeared from radar screens on 8 March 2014, one hour after taking off from Kuala Lumpur for Beijing, told Le Nouvel Observateur that Malaysia was “playing the misinformation game” and he was still not convinced by the crash theory.

“They’ve lied from the first day,” Wattrelos said. “Everyone is lying. The aircraft was hijacked, that’s obvious! The transponders were cut and the plane took an intelligent trajectory flying close to borders to avoid radars. Clearly there was someone at the controls.”

He added: “I’m waiting for irrefutable proof of what’s happened and right now we’re far from that. If they find more debris, I might believe it was a crash but only if they tell me why, how and where. Otherwise, I will continue believing they’ve lied to us since the beginning. We all need to know what happened … it’s not possible for an aircraft to disappear like that.” The Guardian