Lille mayor Martine Aubry, a leading member of the ruling Socialist Party, has filed a case with the police after Grégory Chelli, whose online name is Ulcan, announced on Facebook that he had unearthed her address and phone number but had “not yet decided what punishment would be appropriate for her”.
The city authorities have also filed a complaint, officials confirmed on Friday.
At the beginning of October Lille city council announced that it was putting the twinning process with the Israeli town of Safed “temporarily on standby” because of the Israeli bombing campaign against the Gaza Strip.
Chelli posted his threat on 9 October and the complaints were filed later in the month, although the news did not become public until Friday.
Ulcan, who describes himself as a “Zionist activist” and lives in the Israeli town of Ashdod, has launched cyberattacks against several websites, including those of public radio stations France Inter and France Info and online news and views portal Rue89.
French authorities are pursuing him for cyberpiracy and intentional violence.