Russia is preparing a lawsuit against Ukraine for Kyiv's failure to buy the volume of natural gas specified in the 2009 contracts signed by former Prime Minister Yulia Tymoshenko, Leader of the Party of Regions parliamentary faction Oleksandr Yefremov has said.

"At present, according to my information, the Russian Federation is preparing a lawsuit, which will be filed at a Swedish court. I do not know whether it is reality so, but we have received such information. [The lawsuit] for $10 billion is related to the contract signed by Tymoshenko with the Russian Federation, for gas that we have not bought from Russia," Yefremov told reporters at a briefing in Kyiv on Thursday.