Russian President Dmitry Medvedev said he looked forward to settling rows over energy matters with Ukraine but noted Kiev shouldn't expect any favors.
Ukrainian officials are pressing for better prices for natural gas from Russia. The government says a 2009 deal is unfair. Former Ukrainian Prime Minister Yulia Tymoshenko was sentenced to seven years in prison for her role in the deal.
Medvedev in August said Ukraine could get a better deal if it joined the Moscow-led Customs Union. Kiev said it didn't want to become a full member, however, because it would interfere with free trade deals with the European Union.
"I told (Ukrainian President Viktor) Yanukovych frankly about that," Medvedev was quoted by Russia's state-run news agency RIA Novosti as saying. "Certainly, joining the Customs Union, the European Union or any other union on special terms is impossible."
Brussels has stepped away from Kiev because of the Tymoshenko issue, saying the charges were politically motivated.
Nevertheless, Medvedev said he hoped Russia's Gazprom and Ukraine's Naftogaz would "manage to find such ways of cooperation that would be beneficial, transparent and correct from a legal point of view for both Ukraine and the Russian Federation."