Barrot delivered the warning on the sidelines of a G7 foreign ministers' meeting in Paris.
He named Iran as one place where a repeat attacker might be tempted to act. The remarks as reported did not announce a confirmed perpetrator or a public list of measures already taken.
Barrot cast the French attacks as exceptional in scale and aggression, and tied any reply — public or not — to stopping anyone, in Iran or elsewhere, from trying again.
Hundreds of French stores were affected. The intrusion did not stay on computer systems: it spoiled food that shops then had to discard.
The warning also followed a wider incident. On Nov. 2, stores in at least nine other European countries were hit by a suspected cyberattack on their freezer systems.
The attacks came on Oct. 11 and 12. They raised temperatures in store refrigerators and forced many supermarkets to throw away entire inventories of perishable food.
Barrot said the response would be proportionate and aimed at deterrence."I can also tell you that we rule nothing out and will take all measures – including those we may not disclose publicly – that we deem proportionate and necessary to deter any further attacks,"he added. The goal, Barrot said, is"to deter anyone who might be tempted, in Iran or elsewhere, to do it again.".
"This attack is unprecedented in both its scale and its level of aggression,"Barrot said. France said it ruled nothing out after cyberattacks hit hundreds of French supermarkets, including steps it might not disclose.