France has accused Iran of being behind the massive cyber attack on supermarket fridges last month.
French officials have blamed Iran's Revolutionary Guards for the attacks that knocked out commercial fridges and freezers across France - warning there would be consequences for Tehran.
Iran has routinely denied carrying out malicious cyber operations.
French foreign minister Jean-Noel Barrot said the Iranian ambassador had been summoned to France's foreign ministry.
"This is an attack of unprecedented scale and aggressiveness," Mr Barrot said.
"It is the first large-scale cyber attack aimed at sabotage on French soil, and it represents a major threat to our national interests and the security of the French people. That is why it will not go unanswered."
Mr Barrot also threatened additional EU sanctions against Iran, vowing to take "any other measures needed" to respond to it and deter future attacks.
Paris prosecutor Laure Beccuau said in a statement that a formal judicial investigation was opened on Monday into suspected organised cybercrime with the aggravating circumstance of "having been committed to serve the interests of a foreign power - in this case, Iran".
The investigation targets the leader of Shahid Kaveh, an Iranian group described as a "cyber unit" affiliated with Iran's Islamic Revolutionary Guard Corps, as well as his two deputies and any other persons who may be identified in connection with the case.
Investigators found the attackers had used Farsi and IP addresses linked to devices located in Iran, Ms Beccuau said. The Paris prosecutor's office is seeking international arrest warrants, she added.
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The 11 October cyber attack, which overrode the temperature controls on commercial fridges in hundreds of establishments, appeared to have been easy to carry out, cybersecurity experts previously told Reuters.
The firm behind several of the stricken units said many were obsolete or running outdated firmware, which could have made it easy for hackers to target them.
Some fridges had their temperature switched up so high they caught fire.
In the hours following the hack, supermarket employees carted boxes filled with perished meat and melted ice cream into giant rubbish containers.
Around 700 of the country's 10,000 supermarkets were affected.
The total cost of the attack could amount to tens of millions of euros nationwide, one French supermarket owner estimated.
Last week, another cyber attack in France on several blood banks attempted to raise temperatures to extremely high levels, but was intercepted before it could do any damage to blood products or samples.
France's national cybersecurity agency and Paris prosecutors are investigating.
Also last week, supermarkets in Sweden, Belgium, Luxembourg, Ireland and Estonia were hit by problems with freezers and fridges apparently caused by cyber attacks, forcing some to dispose of perished food.
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