Russia is not demonstrating its readiness to resolve the issue of natural gas shipments to Ukraine and the EU, Ukrainian Prime Minister Arseniy Yatseniuk said in a letter to top European Commission officials and the leaders of EU countries.

In his letter, which addressed the question of natural gas shipments to Ukraine, Yatseniuk said Russia was refusing to participate in a dialogue on the price of gas.

"The answer received from OJSC Gazprom to Naftogaz Ukrainy's pre-arbitration statement gives evidence of Russia's refusal [to participate in] a dialogue," the letter says.

If Russia refuses to participate in resolving the issue, a lawsuit will be filed with the Arbitration Institute of the Stockholm Chamber of Commerce at the end of May, Yatseniuk said.

"Ukraine is ready to resolve the dispute," he said in the letter, adding that this concerned regulation both inside and outside of court.