Cyberattacks of "unprecedented intensity" have targeted several French government institutions just months before the Paris Olympics but have been contained, the prime minister’s office said Monday.

The latest cyberattack to hit France follows a warning from Attal's defence adviser just last week that the Olympics games in July and European Parliament elections in June could be "significant targets".

Prime Minister Gabriel Attal's office said several state bodies were targeted but did not provide details.

"Many ministerial services were targeted" from Sunday "using familiar technical means but of unprecedented intensity," Attal's office said.

A security source told AFP that the attacks "are not currently attributable to Russia," an obvious suspect for many given Paris' support for Kyiv since the invasion of Ukraine.

The PM's staff added that a "crisis cell has been activated to deploy countermeasures", meaning "the impact of these attacks has been reduced for most services and access to state websites restored."

Specialist services including information security agency ANSSI were "implementing filtering measures until the attacks are over".

Several hacker groups claimed responsibility for the attacks on Telegram, a messaging app, including one calling itself Anonymous Sudan which said it had launched a distributed denial of service (DDoS) attack on French government network infrastructure.

"We have conducted a massive cyberattack... the damage will be widespread," said the group, which posts with an avatar of a hooded Guy Fawkes mask in front of a desert scene with pyramids.

Guy Fawkes is famous for his 1605 plot to blow up Britain's parliament, and his image has become a widespread symbol for revolutionary protest.

"A lot of different digital government sectors have been affected, including very important websites, with their respective subdomains," it said.

Anonymous Sudan is a known outfit that has carried out attacks in the past year against websites in countries including Sweden, Denmark and Israel.

Purportedly based in Sudan, it says it targets what it deems to be anti-Muslim activity with some signs that it is sympathetic to Russia.

Specialist website Numerama said Anonymous Sudan's exact motivations were "unclear", adding however that it had a track record of "targeting enemies designated by Moscow". 

A DDoS attack involves using a computer or network of computers to make a massive number of requests of a target system, overwhelming its ability to respond to legitimate users.

According to US cybersecurity firm Cloudflare, Anonymous Sudan is one of many groups employing DDoS attacks and organisations can protect themselves against its methods.

The latest cyberattack also follows a call from Defence Minister Sebastien Lecornu last month to step up protection against "sabotage and cyberattack" by Russia, in an internal note seen by AFP that said his ministry was top of Moscow's target list.