MOSCOW, Russia (AFP)—A cyberattack on Russia’s national airline Aeroflot grounded 42 flights on Monday, officials said, with a Ukrainian and a Belarusian hacker group claiming responsibility for the incident.

Air travel disruptions have become common in Russia since the Ukraine conflict began, often due to Ukrainian drones cutting through airspace, but this is the first time a cyber attack has caused disruption of this scale.

Russia’s state prosecutor’s office said it had opened a criminal investigation after flights were disrupted at Moscow’s Sheremetyevo airport, one of the capital’s three air hubs and Aeroflot’s main base.

“The cause was a failure in Aeroflot’s IT system due to a hacking attack,” it said.

Ukrainian hacking group “Silent Crow” and Belarusian group “Cyber Partisans” claimed responsibility in a joint statement.

“We announce the successful completion of a long-term and large-scale operation that resulted in the complete compromise and destruction of the internal IT infrastructure of Aeroflot,” they said.

The hackers claimed to have “destroyed” 7,000 of the carrier’s servers and suggested they would publish the personal data of all Russians who had flown with Aeroflot.

The carrier said it was “working to restore normal operation as quickly as possible.”

The Kremlin said it was alarmed by the incident.

“We will, of course, clarify the information and wait for an appropriate explanation,” spokesman Dmitry Peskov told reporters.

Ukraine and its allies have long accused Russia of state-backed cyberwarfare, disrupting government and private IT systems around the world and damaging critical infrastructure.

European anti-crime body Europol said this month it had dismantled a pro-Russian hacking group accused of launching thousands of online attacks against Ukraine and its allies.