The Ukrainian Interior Ministry has opened a criminal inquiry against the national joint-stock company Naftogaz of Ukraine's former management on charges of abuse of office, Ukrainian Interior Minister Arsen Avakov said on Facebook on Sunday evening.

The suspects colluded with the managers and shareholders of RosUkrEnergo and Group DF in 2010 when the International Court of Arbitration in Stockholm obliged Naftogaz to return 12.1 billion cubic meters of gas to RosUkrEnergo, he said.

"We suspect the national company's former management of having colluded with the shareholders and executives of RosUkrEnergo and Group DF, and Centragas Holding AG which owns a 50% stake in RosUkrEnergo, co-owned by the Russian gas company Gazprom," Avakov said.

The Interior Ministry's claims against these companies boil down to the following, he said. "In late 2010, the International Court of Arbitration in Stockholm passed a ruling on the dispute between RosUkrEnergo and Naftogaz of Ukraine over the expropriation of 11 billion cubic meters of gas. Naftogaz was obliged to return 12.1 billion cubic meters of gas from Ukrainian underground storage facilities to RosUkrEnergo, including 1.1 billion cubic meters in penalty."

Avakov also said that this court ruling was passed only "when the Naftogaz management, presumably on the Ukrainian leadership's orders, colluded with [Dmytro] Firtash [a Ukrainian businessmen and a RosUkrEnergo's shareholder] and with related structures. Naftogaz suddenly reversed its position in court and… lost. What was the price of the issue? Dozens of billions," Avakov said.

The Interior Ministry's investigative department has obtained fresh information on this collusion. "An inquiry has been started and referred to the Prosecutor General's Office. Jointly with the Prosecutor General's Office we are planning an investigation into this high-profile case," he said.