A cyberattack of "unprecedented intensity" against the French government claimed by pro-Russian hackers this week failed to stop state operations running, a minister said Friday.

The attack came just months before Paris hosts the Olympics Games in July.

The 48-hour effort that started Sunday "hit 800 administrative centres at once" but "at no moment were communications down... every civil servant was well-informed in real time and it did not destabilise the functioning of the state," Civil Service Minister Stanislas Guerini told reporters in Rennes, northwest France.

It had been "an attack of unprecedented scale in intensity, in time, and the number of places targeted," he added during a visit to a government network centre.

Guerini said he was "very cautious" about identifying the perpetrators of the attack, which was claimed by a pro-Russian group calling itself Anonymous Sudan.

"Several names have been mentioned: what stands out to me is Anonymous rather than Sudan," Guerini said, saying those behind it were "almost certainly in allegiance to pro-Russian networks".

The hackers had claimed they launched a "massive cyberattack" against France's economy, culture and environment ministries, as well as the prime minister's office and the DGAC civil aviation authority.

"Ties between these networks of cybercriminals and Russian networks are known and documented, acknowledged," Guerini said, adding that "all of this is part of the hybrid war our nations are already experiencing."

President Emmanuel Macron on Thursday highlighted "hybrid" attacks originating from Russia -- including against French hospitals -- in a prime-time TV interview explaining his support for Ukraine against Moscow's invasion.

Europe should be "ready to respond" to any Russian "escalation" of the conflict, Macron said, after weeks of criticism for refusing to rule out sending troops into Ukraine.