Britain has blamed Russia for a cyberattack last summer that disrupted companies across Europe, warning that the West will not tolerate such "malicious" activities.
The Foreign Office said on February 15 that “the Russian government, specifically the Russian military,” was responsible for the so-called NotPetya ransomware attack in June.
"The decision to publicly attribute this incident underlines the fact that the U.K. and its allies will not tolerate malicious cyberactivity," a statement said.
British Defense Secretary Gavin Williamson said Russia was "ripping up the rule book" and that London had the duty to respond.
Williamson accused Russia of "undermining democracy, wrecking livelihoods by targeting critical infrastructure, and weaponizing information."
He warned that the West is facing "a new era of warfare, witnessing a destructive and deadly mix of conventional military might and malicious cyberattacks."
Russian President Vladimir Putin’s spokesman, Dmitry Peskov, rejected Britain’s allegations as groundless, asserting that they were part of what he called a "Russophobic" campaign being conducted in some Western countries.
Russia has denied responsibility for the NotPetya attack in the past and has pointed out that Russian companies were among those affected.
The NotPetya cyberattack started in Ukraine, where it crippled government and business computers before spreading across Europe and elsewhere. It is estimated to have cost companies more than $1.2 billion.
A number of European companies were badly affected, including Britain-based consumer goods maker Reckitt Benckiser, which said its manufacturing output and shipping capacity were disrupted for up to two months and contributed to a fall in revenues.
Russian state oil company Rosneft and U.S. pharmaceutical giant Merck were among the businesses also hit by the attack.
"The attack masqueraded as a criminal enterprise, but its purpose was principally to disrupt," the British Foreign Office said.
"Primary targets were Ukrainian financial, energy, and government sectors,” the statement added. “Its indiscriminate design caused it to spread further, affecting other European and Russian businesses."
In November, Prime Minister Theresa May accused Putin of attempting to "sow discord" in the West by meddling in elections, spreading misinformation, and engaging in cyberwarfare.
In a report released in January 2017, U.S. intelligence agencies concluded that Russia -- on President Vladimir Putin's orders -- engaged in a hacking-and-propaganda effort aimed at influencing the U.S. presidential election in 2016.
The U.S. Justice Department and three different congressional committees are investigating the alleged Russian meddling and whether there was collusion between Russians and current and past associates of President Donald Trump.
Russia denied it meddled, and Trump says there was no collusion.
Allegations of malicious Russian cyberactivity have added to tension between Russia and the West, whose relations have been badly strained by disputes over issues including Moscow's military intervention in Ukraine and Syria.
With reporting by Reuters and the BBC