Russia's gas export monopoly Gazprom has threatened to halt gas supplies to Ukraine over $1.5 billion of debt for earlier deliveries.
Gazprom, the world's largest gas producer, supplies a quarter of Europe's gas needs via Ukraine and Belarus. Previous pricing disputes have led to cuts in deliveries to Europe, but the EU said Gazprom had given assurances this time.
Russia has been involved in repeated disputes with the countries through which it ships its gas to Europe and which received Russian gas at subsidised prices.
A new Ukraine government has recently sought to revise terms of its gas agreement. Ukraine's pro-Western President Viktor Yushchenko is due to visit Moscow next Tuesday.
The disputes raise concerns in Europe over supplies, particularly in the middle of winter, but the European Commission said Gazprom had given assurances that its dispute with Ukraine would not affect supplies to the EU. Some 80% of Russia's gas exports to Europe go through Ukraine.
