Ukraine has alleged that Russian security services were involved in launching a massive cyber attack which locked up computers across the world.
The Ukrainian security agency, known as the SBU, said similarities between the malicious software and previous attacks on Ukrainian infrastructure shows Russian intelligence services took part.
Ukraine was one of countries hardest hit by the attack 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 attack.
Relations between Russia and Ukraine have collapsed since Moscow annexed Crimea in 2014 and began backing separatists fighting forces loyal to Kiev in eastern Ukraine.