National joint-stock company Naftogaz Ukrainy has said that the litigation with Russia over Naftogaz assets in Crimea could start in summer, Naftogaz Board Chairman Andriy Kobolev told reporters on Wednesday.

He said that the lawsuit will be international investment arbitration.

"Claims have been sent to the Russian Federation… The process has been launched. I think it [the start of the action] will take two or three months," Kobolev said.

He said that Russia can bring counter offers to Ukraine on compensation of Crimean assets of the Ukrainian holding before the arbitration is commenced.