Photo from Kintarojoe via flickr.com

"It is noted that the hacker attack most likely took place in cooperation with the Russian special services," Artyom Minyailo said at a briefing, Reuters said.

Read alsoReuters: Russian hackers targeted Ukrainian company at center of impeachment storm

Energy company Burisma Holdings was at the center of attempts by President Donald Trump last July to ask Ukrainian authorities to announce an investigation into Hunter Biden, the son of Democratic U.S. presidential contender Joe Biden.