Ukraine says it has proof that Russian security services were involved in the cyber-attack that targeted businesses around the world earlier this week.
The country’s security service, the SBU, said it had obtained data that points to a link with an attack on the nation’s capital, Kiev, in December.
Ukrainian firms were among the first to report issues with malicious software on Tuesday, before the virus spread.
Moscow denied any involvement, adding that the allegations were “unfounded”.
The virus, which disrupted IT systems across the globe, froze computers and demanded a ransom be paid in the digital currency Bitcoin, which is untraceable.
However, the attack also hit major Russian firms, leading some cyber security researchers to suggest that Moscow was not behind it.
But on Saturday, Ukraine’s SBU said in a statement that – through data obtained from international anti-virus companies – it had established a connection with a previous attack involving the so-called Petya virus, which it alleges was not designed to secure ransom payments.