MOSCOW, May 14 -- Russia said Wednesday it would resume gas price talks with Ukraine if Kiev pays off part of its mounting gas debt, in an apparent move to soften its tone in gas disputes with the Eastern European country.

"No one ever said: Return four billion U.S. dollars immediately, " Prime Minister Dmitry Medvedev told reporters. But he stressed that Ukraine should at least show the willingness to pay the outstanding debt.

"If they pay a part, it is at least a basis for talks," the Itar-Tass news agency quoted him as saying.

Russian state-run gas monopoly Gazprom almost doubled Ukraine's gas debt to 3.505 billion dollars after Moscow raised gas prices for Ukraine sharply following massive protests that overthrew former Ukrainian President Viktor Yanukovich.

Medvedev said Russia was "even ready to sacrifice our own interests to some degree" over further gas cooperation, but said the European Union (EU) should also persuade Kiev to single out some money received from the bloc to pay the debt.

Ukraine struck deals with the EU for loans worth more than 1.35 billion euros (1.85 billion dollars) for state building and economic reform on Tuesday.

Earlier the week, Gazprom CEO Alexei Miller informed its Ukrainian counterpart Naftogaz that supplies of gas will be conducted under prepay option starting June. Under that scheme, Naftogaz must prepay to the Russian supplier 1.659 billion dollars before June 2 for 3.42 billion cubic meters of gas.

In 2010, Russia and Ukraine signed a gas-for-fleet agreement, under which Moscow offered a discount for gas in exchange for extending its lease of the Black Sea fleet in Crimea for another 25 years.

In April, Moscow declared the pact no longer valid as Crimea joined Russia in March. Following the announcement, Gazprom canceled discounts on gas supplies to Ukraine and set a price tag of 485 dollars per thousand cubic meters, which Kiev has called overpriced and temporarily suspended gas intake.