Ukraine said  it had uncovered clues Russia could have been behind a cyber attack that knocked out government websites in Kyiv at a time of mounting tensions between both neighbours.

The “investigation is still ongoing but the security service of Ukraine has obtained preliminary indicators suggesting that hacker groups associated with the Russian secret services may stand behind today’s massive cyber attack on government websites”, foreign ministry spokesman Mr Oleg Nikolenko said on Twitter.

A statement from the SBU security services said the attacks in the night of Thursday to Friday targeted a total of 70 government websites.

Ten had been subjected to “non-authorised interference”, it said, but their content was not modified and there had been no leaks of personal data.

The hacking came as tensions simmer between Ukraine and Russia, which Kyiv accuses of having massed troops on its border ahead of a possible invasion.

The foreign ministry earlier described the attack that brought down its site and other government portals as “massive”.

On Friday, several websites including the foreign ministry’s were down, an AFP reporter said.

Before it dropped offline, the ministry’s website displayed a message in Ukrainian, Russian and Polish warning Ukrainians that their personal data had been compromised.

“All information about you has become public, be afraid and expect the worst,” the message read.

Within hours of the breach early Friday, the SBU said access to most hit sites had been restored and that the fallout was minimal.

Moscow says it has no plans to invade Ukraine.