SOFIA (Reuters) - Bulgaria has revoked the Bulgarian citizenship of Russian telecoms millionaire Sergei Adoniev over a 20-year-old fraud conviction in the United States, the justice ministry said on Wednesday.

Eager to join EU’s border-check-free Schengen zone, Bulgaria said on Tuesday that it plans to stop letting wealthy foreigners buy citizenship -- which allows free movement within the entire European Union -- in return for investment.

A ministry spokeswoman confirmed a report by Radio Free Europe/Radio Liberty that Adoniev’s citizenship had been revoked in May following notification that he “had been convicted in the United States 20 years ago on fraud charges”.

Adoniev, 57, co-founded the Russian mobile operator Yota, which he sold to Russian billionaire Alisher Usmanov’s Megafon. He also has a stake in the Russian smartphone maker Yota Devices.

He was ranked by the Russian edition of Forbes magazine as Russia’s 147th richest businessman, with an estimated net worth of $700 million, and sponsored one of the candidates in last year’s Russian presidential election, Ksenia Sobchak. He was granted a Bulgarian passport in 2008.

Adoniev was not immediately available for comment.

The Bulgarian non-governmental Anti-Corruption Fund (ACF) alerted authorities to Adoniev’s conviction last January. It also questioned whether foreigners were being properly vetted before seeking citizenship.

According to ACF, Bulgaria has granted 225 passports to foreigners for special contributions in the past 10 years, 125 of them to Russian citizens.