Russia is the most unequal major economy in the world, with almost two-thirds of its wealth controlled by millionaires, a wealth research company has said.

Sixty-two percent of Russia's wealth is held by U.S. dollar-millionaires and 26 percent of its wealth is held by billionaires, New World Wealth said in a report on Wednesday. Russia's economy is climbing out of recession and the International Monetary Fund sees it growing by 1 percent in 2017.

"If millionaires control over 50 percent of a country's wealth then there is very little space for a meaningful middle class," New World Wealth said.

Japan — the world's third-largest economy — was the "most equal" major country by this measure, with millionaires controlling only 22 percent of total wealth.

The U.S. was "surprisingly equal," with around one-third of total wealth held by millionaires.