PARIS (AP) — A pro-Russian hacking group claimed responsibility for a major cyberattack that halted package deliveries by France’s national postal service just days before Christmas, prosecutors said Wednesday.

After the claim by the cybercrime group known as Noname057, French intelligence agency DGSI took over the investigation into the hacking attack, the Paris prosecutor’s office said in a statement to The Associated Press.

The group has been accused of other cyberattacks in Europe, including around a NATO summit in the Netherlands and French government sites. It was the target of a big European police operation earlier this year.

Central computer systems at French national postal service La Poste were knocked offline Monday in a distributed denial of service, or DDoS, cyberattack that still wasn’t fully resolved by Wednesday morning, the company said.

Postal workers couldn’t track package deliveries, and online payments at the company’s banking arm were also disrupted. It was a major blow to La Poste, which delivered 2.6 billion packages last year and employs more than 200,000 people, during the busiest season of the year.

France and other European allies of Ukraine allege that Russia is waging a campaign of “hybrid warfare” to sow division in Western societies and undermine their support for Ukraine. The AP has tracked more than 145 incidents including sabotage, assassinations, cyberattacks, disinformation and other hostile acts that are increasingly draining police resources.