MOSCOW - Russian President Dmitry Medvedev said on Wednesday it would be irresponsible to amend gas supply contracts with Ukraine, in a sign that Moscow will offer no more concessions to its ex-Soviet neighbour on gas payments.

Medvedev, addressing a media forum, said Ukraine had shown it was capable of paying for Russian gas under the terms agreed in a 10-year pact signed in January to end the gas war which damaged industry and left millions of Europeans without heating.

We have signed a treaty this year for 10 years ... I think that proposals to change them are irresponsible, Medvedev said. He made no reference to any specific moves to alter the contract.

European consumers reliant on Russian supplies via Ukraine for one-fifth of their gas want no repeat of the New Year dispute, which shook confidence in Russia's ability to supply gas and the ability of Kiev to give it safe passage.

Russian gas export monopoly Gazprom has relaxed demands on Ukraine's crisis-hit economy, allowing Kiev to buy 35 percent less gas next year than originally contracted and waiving fines on this year's supplies.

Ukraine has made all its monthly payments to Gazprom on time and President Viktor Yushchenko showed rare unity with Prime Minister Yulia Tymoshenko when assuring the European Union last week that Kiev would secure gas transit.

Despite talk that something is happening, that the (Ukrainian) president is not working, the Ukrainians are paying every month and this makes me happy, Medvedev said.

Our EU partners say this isthe result of their work with them. They say the Ukrainians have money, he said.

The 10-year contract stipulates that Ukraine will switch to paying market price for Russian gas from Jan. 1, 2010, after enjoying years of cut-price supplies. In 2009, Ukraine has been paying a 20 percent discount to the European price formula.

I hope Ukraine's switch to market prices will be painless, Medvedev said. I think that, in general, if our Ukrainian partners show responsibility, everything will be alright. (Reporting by Robin Paxton and Denis Dyomkin)