A debt of Russia's Gazprom to national joint-stock company Naftogaz Ukrainy in three months of the non-execution of the award of the Arbitration Institute of the Stockholm Chamber of Commerce to pay $2.56 billion to the Ukrainian company has expanded by almost $50 million, according to calculations by Interfax-Ukraine.

According to the arbitral award, the penalty is imposed on the Gazprom's debt, being $526,000 a day. Thus, in the period from March 1 through May 30, the debt of the Russian company grew by $47.866 million (around UAH 1.25 billion).

As reported, a Stockholm arbitration court ordered Gazprom to pay Naftogaz Ukraine a penalty of $4.7 billion.

Earlier a source in the Ukrainian government has told Interfax-Ukraine that Naftogaz Ukrainy has started recovering a debt of $2.6 billion from Russia's Gazprom in foreign courts to execute the award of the Arbitration Institute of the Stockholm Chamber of Commerce. The source said that the company is working in Switzerland, the Netherlands and the U.K. under Article 5 of the New York Convention on the Recognition and Enforcement of Foreign Arbitral Awards.