Ukraine is sending its energy minister to Russia to try to resolve a worsening dispute over gas prices, days before a deadline to agree new terms expires.
The proposed price rises have roused passions in Ukraine
This follows phone contacts between the two countries' leaders on Tuesday.
Russia's energy minister earlier said no new proposals would be put forward. It wants Ukraine to pay market rates and is seeking a huge gas price rise.
Gas monopoly Gazprom has threatened to cut Ukraine's supplies altogether if new terms are not agreed by 1 January.
The Russian and Ukrainian president discussed the stand-off in a telephone conversation on Tuesday and it was later announced Ukraine's Energy Minister Ivan Plachkov would have new talks in Moscow on Wednesday.
Russia wants to more than quadruple the price of supplies to the Ukrainian market, to between $220 and $230 per 1,000 cubic metres.
Ukraine says it is happy to pay market rates, but wants price increases to be phased in gradually over several years.
"Russia has already made all its proposals. They are included in drafts agreements and contracts, and there will be no other proposals from Russia," Industry and Energy Minister Viktor Khristenko said.
Gazprom on Tuesday denied reports of a deal to raise prices gradually and also dismissed a claim by Ukraine to be legally entitled to take 15% of Russian gas transiting western Europe as payment for pipeline use.
"This irresponsible and legally ignorant announcement is aimed at escalating tension in Russian-Ukrainian relations and undermines Europe's trust in Ukraine as a transit country," a Gazprom statement said.
"All of Ukraine's actions on siphoning off gas after January 1, 2006 will be regarded as... theft," said Gazprom spokesman Sergei Kupriyanov.
Moscow also warned Kiev against any attempt to link the gas price row to rents charged for Russian naval use of Ukrainian port facilities in the Black Sea.
Some Ukrainian officials have suggested such a move as the gas row intensified.
But Russia's defence minister warned that any such increase could have serious consequences.
"The agreement on the Black Sea fleet base is one part of a bilateral treaty, the second part of which contains recognition of mutual borders," Sergei Ivanov said.
"Trying to revise the treaty would be fatal."