A view of the Russian gas giant Gazprom's recently built Adler thermal power plant in the Russian Black Sea resort of Sochi.

Russia raised the gas price for Ukraine on Thursday for the second time this week, almost doubling it in three days and piling pressure on a neighbor on the brink of bankruptcy in the crisis over Crimea.

The increase, announced in Moscow by Russian natural gas producer Gazprom, means Ukraine will pay 80 percent more for its gas than before the initial increase on Monday.

Prime Minister Arseny Yatseniuk said the latest move, two weeks after Moscow annexed Ukraine's Crimea region, was unacceptable and warned that he expected Russia to increase pressure on Kiev by limiting supply to his country.

Read More Russia tightens squeeze on Ukraine with gas price rise

"There is no reason why Russia would raise the gas price for Ukraine... other than one - politics," Yatseniuk told Reuters in an interview in the Ukrainian capital Kiev.

"We expect Russia to go further in terms of pressure on the gas front, including limiting gas supplies to Ukraine."