The Ukraine government claimed that it is almost guaranteed Russia was behind the attack which targeted around 70 government websites in Ukraine. Oleksiy Danilov, Secretary of the National Security and Defence Council of Ukraine said he is “99.9% sure” Russia is behind the attack.
On Friday, about 70 government websites were temporarily down, in the largest such attack on Ukraine in four years.
Before the sites went offline, a message appeared warning Ukrainians to “prepare for the worst”.
Access to most of the sites was restored within hours.
The US and NATO condemned the attack and have offered support to Ukraine, while Russia has not yet commented on the hack.
Mr Danilov further told Sky News: “We can clearly track their signature. These are the Russian specialists who perform these actions.”
The comments come as Victoria Nuland, the US Under-Secretary of State, claimed Moscow was looking for any excuse to invade.
She also told Sky News: “This is straight out of the Russian playbook: to try to, through sabotage operations, through false flag operations, through blaming the other guy, to create that pretext, to give an excuse to go in, or to make it look like the Ukrainians were the aggressors, when in fact the first aggression was perhaps even done by Russians against Russians, to blame the Ukrainians.
“So it’s all very dangerous in the way they operate.”
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Speaking at the National Security and Defence Council building, within a well-guarded compound in Kyiy, he said that they “should have been asleep at that time as it was 3am”
“Their number one task for today is to rock our internal situation.”
As for whether he thought it was a first shot ahead of a physical attack, Mr Danilov said: “That’s how it is according to the textbook. Destabilisation, destabilisation, destabilisation and afterwards comes action.
“It’s written like that in all the textbooks.”
Ms Nuland who served as former US ambassador to NATO said the situation is “extremely worrying”.
She said: “You know, a nation does not deploy 100,000 troops on the border of another nation and put its saboteurs inside the country without some malign and aggressive intent.
“That is a very expensive and difficult and dangerous operation. So why now?”