Ukraine has said it has “evidence” Russia was behind a massive cyber-attack that knocked out key government websites last week, while Microsoft warned the hack could be far worse than first thought.

“All the evidence points to Russia being behind the cyber-attack,” the Ukrainian digital transformation ministry said in a statement on Sunday.

The SBU security service said the attacks in the early hours of Friday had targeted a total of 70 government websites.

The company said it continued to analyse the malware and warned it could render government digital infrastructure inoperable.

It said it had not yet identified a culprit behind the attacks but warned that the number of affected organisations could prove larger than initially thought.