"If our Ukrainian partners show a sense of responsibility, everything will be alright. Europe will have enough gas, as well as other energy supplies," he told a European and Asian media forum hosted by RIA Novosti.
Medvedev said he was categorically against any review of gas agreements with Ukraine.
"I regard the proposal to review these agreements as absolutely irresponsible," he said.
Russia's Gazprom and Ukraine's Naftogaz agreed in November to reduce Russian gas deliveries by 35% in 2010, from the previously contracted 52 billion cubic meters to 33.75 bcm.
The Russian gas monopoly said on Monday Ukraine's reduced demand for gas will cost it $1.3 billion in 2009.
Instead of 40 bcm of gas contracted for 2009, Ukraine will buy less than 25 bcm. But Russia has said it will not fine Kiev for falling short of contracted volumes due to the ex-Soviet state's difficult economic situation.
Russia, which supplies around one quarter of Europe's gas, briefly shut down supplies via Ukraine's pipeline system at the start of the year amid a dispute unpaid bills and new prices.
The conflict was resolved in January, when Putin and Tymoshenko reached a deal on imports and transit for 2009.
Ukraine transits around 80% of Russia's Europe-bound gas.
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