Ukrainian websites have been under nonstop attack from Russian hackers since the Kremlin launched an attack of the country last month, Kyiv's cyber watchdog agency said on Saturday.

In a post to Twitter, Ukraine's State Service of Special Communications and Information Protection said that "Russian hackers keep on attacking Ukrainian information resources nonstop".

The agency said that sites belonging to the presidency, parliament, the cabinet, the ministry of defense and the ministry of internal affairs were among those hit by distributed denials of service (DDoS) which work by directing a firehose of traffic towards targeted servers in a bid to knock them offline.

The agency said the sites were so far weathering the storm.

"We will endure! On the battlefields and in the cyberspace!" it said.

Russian sites have also been hammered with DDoS attacks. Ukraine has called on its hacker underground to help protect critical infrastructure and conduct cyber spying missions against Russian troops.

On Friday Russia's National Coordinating Center for Computer Incidents said there had been "massive computer attacks" on Russian information resources.