Moscow - Ukraine accused the Russian security services on Saturday of planning and launching a massive cyber attack that locked up computers across the world.
The Ukrainian security agency, known as the SBU, alleged in a statement that similarities between the malicious software and previous attacks on Ukrainian infrastructure showed the participation of the Russian intelligence services.
The SBU added the attackers appeared uninterested in making a profit from the ransomware programme and were more focused on sowing chaos in Ukraine.
There was no immediate official response from the Russian government, but Russian lawmaker Igor Morozov told the RIA Novosti news agency that the Ukrainian charges were "fiction" and that the attacks were likely the work of the United States.
Ukraine was the country hardest hit by the attack that started on Tuesday, when computers at government agencies, energy companies and cash machines were temporarily disabled as their data was encrypted amid demands for ransom payments.
Russian companies, including the state-owned oil giant Rosneft, also said they were hit by the cyber attack.
Most of the organisations affected by the attack recovered within 48 hours.
Ukraine has repeatedly accused Russia of sponsoring hacking attacks, including the hack of Ukraine's voting system ahead of the 2014 national election and an assault that knocked its power grid offline in 2015.
Relations between Russia and Ukraine collapsed when Moscow annexed Ukraine's Crimean Peninsula in 2014 and began backing separatists fighting forces loyal to Kiev in eastern Ukraine. That fighting has left over 10 000 people dead since April 2014.