Russia is carrying out a sustained campaign of cyber attacks targeting democracy and critical infrastructure in the West, UK Defence Secretary Sir Michael Fallon has warned.
Moscow was “weaponising misinformation” in a bid to expand its influence and destabilise Western governments and weaken Nato, he said.
Vladimir Putin had chosen to become a “strategic competitor” of the West.
Sir Michael said it was vital alliance members strengthened cyber defences.
His speech, at the University of St Andrews, came hours before Theresa May was due to use an informal summit in Malta to press EU Nato members to boost defence spending.
Meanwhile, in a report, MPs have warned that a skills shortage and “chaotic” handling of personal data breaches are undermining confidence in the UK government’s ability to protect its own infrastructure and economy from cyber attacks.
Sir Michael said Nato needed to do more to tackle the “false reality” being propagated by the Kremlin.
“Nato must defend itself as effectively in the cyber sphere as it does in the air, on land, and at sea, so adversaries know there is a price to pay if they use cyber weapons,” he added.
The defence secretary pointed to a “persistent pattern of behaviour” by Moscow, highlighting a series of cyber attacks that had been linked to Russia.
Suspected Russian attacks included France’s TV5Monde broadcaster being taken off air in April 2015 – originally claimed by hackers linked to the self-styled Islamic State – and the targeting of Germany’s lower house of parliament, he said.
Another cyber attack, on Bulgaria in October 2016, was described by the country’s president as the “heaviest” and most “intense” to be conducted in south-eastern Europe.
Sir Michael also spoke of the suspected Russian hacking of the two main political parties in the US presidential elections.
Russia has denied any involvement in the hacking, and WikiLeaks founder Julian Assange says Moscow was not the source for the site’s mass leak of emails from the Democratic Party.
Sir Michael said: “Today, we see a country that in weaponising misinformation has created what we might now see as the post-truth age.
“Russia is clearly testing Nato and the West. It is seeking to expand its sphere of influence, destabilise countries and weaken the alliance.
“It is undermining national security for many allies and the international rules-based system.
“Therefore it is in our interest and Europe’s to keep Nato strong and to deter and dissuade Russia from this course.”
Sir Michael backed US president Donald Trump’s call for all Nato member states to honour the commitment to spend a minimum of 2% of GDP on defence.