The UK has accused Russia of being behind last year's so-called "NotPetya" cyber attack, which allegedly started in Russia and Ukraine before spreading worldwide, affecting thousands of computers.
The malicious software in June crippled government and business computers in Ukraine before spreading around the world, halting operations at ports, factories and offices.
"The UK government judges that the Russian government, specifically the Russian military, was responsible for the destructive NotPetya cyber attack of June 2017," Foreign Office minister Tariq Ahmad said.
British Defense Secretary Gavin Williamson said the attack was further evidence of a "new era of warfare" with "a destructive and deadly mix of conventional military force and malicious cyber attacks."
"Russia is ripping up the rule book by undermining democracy, wrecking livelihoods by targeting critical infrastructure and weaponizing information," he said.
Moscow immediately denied the accusation, saying it was part of “Russophobic” campaign it said was being waged by some Western countries.
Russia has previously denied being behind the attack, and on Thursday Kremlin spokesman Dmitry Peskov said Moscow “categorically denies the allegations.”
“We consider (them)... groundless. This is nothing more than a continuation of a Russophobic campaign that is without proof,” Peskov told a conference call with reporters.
The attack contaminated thousands of computers across the globe, particularly affecting multinational companies and critical infrastructure.
The malware makes computers inoperable by encrypting their hard drives and demands ransoms in exchange for a digital key to restore access.
According to IT security experts, the virus is a modified version of the so-called Petya ransomware, similar to WannaCry virus, which targeted 200,000 computers in more than 150 countries in May and demanded money from victims in exchange for their data.
The cyber attack first hit computer networks of Ukraine’s central bank and several other financial institutions, the state energy distributor and Kiev's main airport.
However, Russia turned out to be another victim of the attacks with the country’s biggest oil company, Rosneft, and metal maker firm Evraz being targeted.