An outspoken former economic adviser to Russian President Vladimir Putin resigned this week to protest what he calls "a lack of political freedom" in Russia. Andrei Illarionov says the final straw was the bitter dispute between Ukraine and Russia over natural gas prices.

Former Kremlin adviser Andrei Illarionov says Russia's attempt to more than quadruple gas prices for Ukraine amounts to a resurgent Russian imperialism.

Mr. Illarionov said Saturday he decided to resign earlier this week, when he was asked to present the price hike as purely an economic measure.

Russia's giant state-run energy company, Gazprom, has threatened to cut off gas supplies to its neighbor, if Ukraine does not agree to pay four times more for its gas.

Ukraine wants any price increase to be gradual, and does not accept Russia's argument that the steep price increase is only economic.

The move comes one year after the Kremlin lost a battle of wills in the so-called Orange Revolution that brought pro-Western Viktor Yushchenko to power.

President Putin quickly accepted Mr. Illarionov's resignation soon after the 44-year-old economist offered to leave his post as Kremlin adviser.

Mr. Illarionov was one of the longest serving officials within the Kremlin, but he says he long had doubts about the direction Russia is heading under Mr. Putin.

He says that, as long as one "has an opportunity to fulfill your duties, it makes sense to stay in your position and do what you think is right."

But, he says, when those opportunities are gone, "you must leave."

In the past, he has said Russia is lacking in freedom, and has moved from being partially free to no longer free.

Analysts say Mr. Putin kept Mr. Illarionov in the Kremlin to demonstrate some criticism of his policies is tolerated.

"He might be a symbol that some kind of discussion in decision-making still remains within the Kremlin, but I would reduce Illarionov to a puppet," said Boris Makarenko, with the Political Science Center in Moscow.

Many foreign leaders have also expressed concern that Russia is backtracking on democratic reforms under Mr. Putin's leadership.