Russian Prime Minister Dmitry Medvedev says Moscow will resume energy talks with Ukraine if Kyiv repays part of its natural-gas debt.
Medvedev said on May 14 that Russia could also consider revising the high price increase it put on gas sold to Ukraine, saying "it is possible."
Russian gas giant Gazprom says Ukraine owes $3.51 billion for gas.
Gazprom nearly doubled the price of gas for Ukraine after President Viktor Yanukovych was ousted in February, raising it from $268.5 to $485 per 1,000 cubic meters.
Ukrainian officials say $268.5 is fair and have threatened to take Russia to an international court over the steep price increase.
Ukraine is dependent on Russia for more than half of its gas needs and is the gateway for most of the Russian gas that Western Europe uses.
Based on reporting by Reuters and ITAR-TASS