Pro-Russian hackers are believed to have launched cyberattacks against hospitals in the Netherlands and other European countries as revenge for their support for Ukraine.

Z-Cert, an organisation that specialises in digital security in the healthcare sector, said Groningen’s UMCG teaching hospital had been hit by a DDoS attack that had taken down its website.

On Monday the website’s home page carried a message saying it was unavailable. ‘We are working hard on a solution, but are unable to indicate how long this will take,’ it said.

The hospital was one of several institutions targeted by Killnet, a Russian group that specialises in distributed denial of service (DDoS) attacks, in which a website is overwhelmed by a surge of access requests from large numbers of computers at once.

RTL said Killnet, which has 92,000 people in its online chat group, had also called for supporters to attack hospitals in Utrecht, Rotterdam and Nijmegen.

‘It’s very simple,’ the founder of Killnet wrote in the group chat. ‘We are destroying the medical facilities in these countries for their support for the Nazis in Ukraine.’

A spokesman for UMCG said only the publicly accessed section of its website had been affected by the attack.

‘Patients who want to look up their medical information may have difficulties, for example if they want to know what a particular treatment looks like,’ the spokesman said.