Ukraine said on Sunday it had “evidence” that Russia was behind a massive cyberattack that knocked out key government websites this past week, while Microsoft warned the hack could be far worse than first thought.

Tensions are at an all-time high between Ukraine and Russia, which Kyiv accuses of having amassed troops on its border ahead of a possible invasion. Some analysts fear the cyberattack could be the prelude to a military attack.

“All the evidence points to Russia being behind the cyberattack,” the Ukrainian Digital Transformation Ministry said in a statement. “Moscow is continuing to wage a hybrid war.”

‘Data safe’

The ministry urged Ukrainians not to panic, saying their personal information was protected.

The Kremlin earlier rejected the claims and said there was no evidence Russia was behind the attack. “ Russia has nothing to do with these cyberattacks,” President Vladimir Putin’s spokesman, Dmitry Peskov, told CNN .

But Microsoft warned Sunday that the cyberattack could prove destructive and affect more organisations than initially feared.

The U.S. software giant said it continued to analyse the malware and warned it could render government digital infrastructure inoperable. Microsoft said it had not so far identified a culprit but warned that the number of affected organisations could be larger than initially thought.

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