KIEV, September 20 (RIA Novosti) - Ukraine's president blamed the government for signing a gas contract with Russia that he deems inappropriate and reiterated that it could be revised at any time.

"The agreement can be revised at any moment," Viktor Yushchenko told Bloomberg. "I don't think an agreement based on such non-market principles added any stability to the issue of gas supplies to Europe."

He said the government is "responsible for that" and added that these had been "fatal mistakes" as Ukraine is paid less than any other European country for gas transit. He said this caused the country's gas monopoly Naftogaz to run a deficit of almost $4 billion.

Yushchenko said that should gas transit tariffs be raised to the "lowest possible level European countries pay," Naftogaz would gain $2.5 billion.

Russia and Ukraine signed natural gas contracts in January, ending a dispute between the ex-Soviet allies that interrupted Russian gas supplies to the EU for two weeks earlier that month over a bitter pricing and debt row between Moscow and Kiev.

The contracts have been criticized by Yushchenko, but Prime Minister Yulia Tymoshenko, who plans to stand against him in the January presidential elections, earlier said the deals would remain intact but additional documents could be signed.

She said Kiev would buy around 25 billion cubic meters in 2010, half the agreed amount of gas stipulated in the contract, which runs until 2019. Naftogaz earlier said the transit fee could rise from the current $1.7 to $2.7 per 1,000 cu m per 100 km for Russian gas transits across Ukraine next year.

President Dmitry Medvedev instructed the head of Russia's energy giant Gazprom on September 7 to stick to the current terms of the gas contract with Ukraine regarding transit rates.

Russia supplies about 80% of its Europe-bound gas via Ukraine.