Paris prosecutors opened an investigation after the internet sites of several major French cities were inaccessible on Tuesday following attacks by hackers claiming they were protesting against French support for Ukraine.

At 1600 GMT, the sites of the cities of Marseille and Tarbes were down, as was the site of the department of Haute-Garonne.

The attacks were claimed on X by a hackers group calling themselves NoName, a collective already known for other attacks and for defending Russian points of view.

On their X account, the hackers claimed to have also attacked the sites of cities such as Nantes, Bordeaux, Poitiers, Pau, Nimes, Nice, Angers, Le Havre and Montpellier, as well as the department of Les Landes, French Polynesia and New Caledonia. Nonetheless, all were operational on Tuesday.

The Paris prosecutor’s office said a total of 23 sites were targeted.

The mayor of Nice, Christian Estrosi, confirmed on X that his city's website was one of those.

Marseille's town hall told AFP that the servers that host the city's websites had been subject to attacks that required them to enact "protection mechanisms that had the consequence of making them inaccessible".

The cities of Pau and Angers, as well as the Landes department, said they had not noticed any incidents.

DDoS attacks, or "distributed denial of service", are frequently used by NoName in a technique that involves saturating sites with a huge number of automatic requests that render them inoperable.

The attacks generally do not involve stealing data.

Benoit Grunemwald, a cybersecurity expert at ESET, said that the goal appears to be propaganda by "creating an impression of a climate of digital insecurity". (AFP)