Ukraine says its has obtained proof that Russia's security service was behind last week's Petya/Not Petya malware attack that hit the country's infrastructure particularly hard.

A Kremlin spokesman dismissed Kiev's accusations as "unfounded blanket accusations".  Russian firms were hit in the attack that scored victims around the world, and the malware conked out the computers at an Australian chocolate factory. 

But Ukraine says its state security service SBU has determined that the same Russian hackers who shut down the country's power grid in late 2016 pulled off last week's malware attack. 

"The available data, including those obtained in cooperation 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."

The malware told victims that their files had been encrypted, and the only way to retrieve the information was to pay US$300 in Bitcoin, an untraceable transaction.  But the email address associated with the Bitcoin wallet was closed, leaving no way for victims to pay.  Meanwhile, computers in Ukrainian banks, airports, and public works systems were locked up.

"The virus is cover for a large-scale attack on Ukraine.  This is evidenced by a lack of a real mechanism for taking possession of the funds,"said the SBU, "Enrichment was not the aim of the attack.

"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."

Last week, NATO said the attack is believed to be the work of a state actor and is a potential act of war.