"Naftogaz's revenues make up 8% of GDP, and Ukraine's transit income is 2.3% of GDP", Vitrenko said.
However, on Thursday a spokeswoman for Naftogaz said it had received no gas, despite making a pre-payment for volumes to be delivered in March.
Ukraine is Russia's main gas transit route to Europe, but bilateral relations have been strained for quite a while.
Naftogaz said it now wants to start talks with Gazprom on the post-2019 transit terms, but Gazprom is still unhappy after the court ruling on the current contract. The Russian side has returned the funds to Naftogaz in full.
Gazprom acknowledged the receipt of the money for March to ICIS, but said: "As of today [Thursday], the additional agreement to the actual contract for gas supplies with Naftogaz, which is necessary for the supply start, has not yet been signed".
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According to the court ruling, Naftogaz was granted compensation of 4.63 billion US dollars for the failure of Russia's gas giant Gazprom to supply the contracted volume of gas for transit via Ukraine, said Kobolev. Reverse flows refer to buying Russian gas that has first been exported to another country. "The company sees Gazprom's refusal to deliver prepaid gas as a breach of contract and failure to comply with the arbitrage decision", it said.
"Taking into account the results of the two proceedings regarding the relationship between Gazprom and Naftogaz for supplies and transit, there was a significant imbalance that violated the basic principles of Swedish law, which regulated the contract".
In particular, Naftogaz CEO Andriy Kobolyev informed the president that the company had got the final decision of the Stockholm arbitration tribunal, according to which Ukraine was awarded damages of $4.630 billion that must be reimbursed by Gazprom for the past periods.
It said it would "defend its rights in all ways available to it in accordance with applicable law".
However, the Stockholm arbitration court ruling is being opposed by the Gazprom.