Russian President Vladimir Putin and Ukrainian President Viktor Yanukovych have postponed talks in which they were to discuss a new deal on natural gas supplies and stronger economic ties.
Officials on both sides said Tuesday more time was needed to prepare documents they planned to sign.
The meeting was meant to resolve a gas pricing dispute. Ukraine complains Russia is charging too much for the gas it imports from Russia, but it does not want to institute the closer economic and political ties Russia demands in return. Russia wants Ukraine to join a planned customs union with itself, Belarus and Kazakhstan.
In the past, Russia has cut gas supplies to Ukraine over pricing disputes.