"Today - I stress ahead of schedule - the government has paid for Russian natural gas pumped into storage tanks in Ukraine. We have transferred $605 million and have paid in full," Tymoshenko said.
Russia's Gazprom has so far not confirmed receipt of the funds.
Tymoshenko said that Ukraine would continue to ensure "successful" settlements for gas pumped into underground gas storage facilities.
The European Commission announced late in July it had reached an agreement with Ukraine on the modernization of its gas sector and the readiness of international financial institutions to grant the ex-Soviet republic a gas loan.
The international financial institutions comprising the European Bank for Reconstruction and Development (EBRD), the European Investment Bank and the World Bank are to release a $1.7 billion loan to Ukraine to modernize its gas sector and facilitate payments for gas purchases, a European diplomatic source told RIA Novosti.
Ukraine had earlier sought a loan of over $4 billion from the EU to pump gas into its underground storage facilities to avoid interruptions with gas transit to Europe.
Russia, which supplies around one quarter of Europe's gas, briefly shut down supplies via Ukraine's pipeline system at the start of the year during a dispute with Kiev over gas supply debt.
The conflict was resolved in January, when Russian Prime Minister Vladimir Putin and his Ukrainian counterpart Tymoshenko agreed deals on deliveries to and gas transit through Ukraine for 2009.
The ex-Soviet state transits around 80% of Russia's Europe-bound gas.