Paris (France) (AFP) – Major French supermarket chains Intermarche and Cooperative U were hit by a cyberattack that caused their refrigerators to defrost, the two retailers told AFP Monday.

Some 150-200 Intermarche shops were targeted, along with almost 100 Cooperative U outlets, in the attack, they said.

Paris prosecutors confirmed the attack, which reportedly also hit other major chains, and also indicated it had prompted outbreaks of fire.

BFM TV said France's largest supermarket chain E. Leclerc was also affected, with hackers "managing to remotely trigger the forced defrosting of the refrigeration systems in numerous stores". Contacted by AFP, E. Leclerc did not immediately confirm the information.

Those branches that were affected will have to "throw away all of the products" that are fresh and frozen, Intermarche told AFP.

Specialist French retail sector news website jebosseengrandedistribution.fr said other retail giants Carrefour Market and Monoprix were affected but the companies have yet to confirm this.

The chief executive of Cooperative U, Dominique Schelcher, described the attack as "unprecedented" and confirmed the cyberattack had affected refrigeration systems since Sunday night.

"Targeting equipment essential to the preservation of fresh products and to the food supply of the French people is extremely serious and is unprecedented. It is unacceptable," he wrote on X.

He added that the company's teams are "fully mobilised" to restore the situation as quickly as possible.

"An investigation will be necessary to shed full light on this attack," he added.

The office of the Paris prosecutor confirmed to AFP that an investigation has been opened into "the large-scale cyberattack affecting the refrigerators of several major food retail chains across France".

The probe will help "identify the victims and establish the link with the damage they reported in terms of foodstuff losses and the outbreak of fires", the prosecutor's office said.

Intermarche condemned the food waste and financial losses resulting from the attack, without providing figures, and warned there could be issues with insurance policies which do not "cover this type" of in-store incident.

BFM TV said temperatures were "altered remotely, resulting in the destruction of stocks of fresh and frozen products".

The incident comes against the background of growing concern over the potential havoc that can be caused in Europe in all sectors by cyberattacks by malicious actors.

President Emmanuel Macron, a strong supporter of Ukraine in its fight against the Russian invasion, last month ordered measures to protect France's critical infrastructure from Russian "hybrid attacks".