Ukraine says Russian security services were involved in the recent cyber attack aimed at destroying its important data and spreading panic.
The SBU, Ukraine's state security service, said on Saturday the attack, which started in Ukraine and spread around the world on Tuesday, was by the same hackers who attacked its power grid in December 2016.
Ukrainian politicians were quick to blame Russia for Tuesday's attack but a Kremlin spokesman dismissed "unfounded blanket accusations".
Cyber security firms are trying to piece together who was behind the computer worm, dubbed NotPetya by some experts, which conked out computers, disrupted shipping and shut down a chocolate factory in Australia across an estimated 60 countries.
"The available data, including those obtained in co-operation with international antivirus companies, give us reason to believe that the same hacking groups are involved in the attacks, which in December 2016 attacked the financial system, transport and energy facilities of Ukraine using TeleBots and BlackEnergy," the SBU said.
"This testifies to the involvement of the special services of Russian Federation in this attack."
Russia and Ukraine have been at loggerheads since 2014 when Russia annexed Crimea.
The SBU in an earlier statement on Friday said it had seized equipment it said belonged to Russian agents in May and June to launch cyber attacks against Ukraine and other countries.
"The main purpose of the virus was the destruction of important data, disrupting the work of public and private institutions in Ukraine and spreading panic among the people," the SBU said of the recent attack.
A cyber attack in December on a Ukrainian state energy computer caused a power cut in the northern part of the capital Kiev.
The Russian foreign ministry and Federal Security Service did not immediately respond to requests for comment on the latest allegations.