Ukraine`s Naftogaz owes former gas supply intermediary RosUkrEnergo 12.1 billion cubic metres of natural gas to compensate for fuel it had "expropriated", a RosUkrEnergo shareholder said, citing an arbitration court ruling, according to Reuters.

Centragas, a joint owner of RosUkrEnergo with Russian gas giant Gazprom (GAZP.MM: Quote), said on Tuesday state-owned Naftogaz had taken the gas in January 2009 while it was sitting in Ukrainian underground storage awaiting transit to Europe.

"Today... the Stockholm Arbitration Tribunal made a further award... This award confirms that the gas in question was taken by Naftogaz in breach of its storage contract with RosUkrEnergo and that Naftogaz will return 11 bcm of gas in storage in Ukraine to RosUkrEnergo," Centragas said in a statement.

In addition, Naftogaz must give RosUkrEnergo 1.1 bcm of gas as a penalty, it said.

At the current Russia-Ukraine contract price level, 12.1 bcm of gas would be worth $2.8 billion.

Naftogaz declined to comment on the matter. Ukraine`s government said last year it bought the gas in question from Gazprom for $1.7 billion.

The claims from RosUkrEnergo followed a decision by Ukraine and its supplier Russia to scrap the firm as an intermediary between Gazprom and Naftogaz after a series of rows that briefly halted transit of Russian gas to Europe.

Centragas is 90 percent owned by GDF, a holding company for Ukrainian tycoon Dmytro Firtash.