KIEV, June 16. /ITAR-TASS/. Ukraine’s Naftogaz has filed a lawsuit with the Stockholm Arbitration Court against Russia’s Gazprom to demand gas contract revision, according to the company’s statement. Kiev is set to claim $6 billion of overpayment for natural gas supplied by Russia since 2010.

Earlier, the Russian company has also turned to the international arbitrary court.

Gazprom has filed a $4.5 billion suit against Ukraine’s energy company Naftogaz to the Stockholm arbitration court and switched Ukraine to an advanced payment system, the company said in a statement on Monday.

“Gazprom has turned to the Stockholm international arbitration court with a suit against Naftogaz Ukrainy seeking the recovery of a $4.5 billion debt due to the company’s improper fulfillment of the contract signed on January 19, 2009 on purchasing and selling of gas in the years 2009 through 2019,” the company said.