Russian Economy Minister Alexei Ulyukayev has been detained over a $2 million bribe allegedly received for a “positive” assessment, which led to oil producer Rosneft acquiring a 50 percent stake in Bashneft, the country’s Investigative Committee said on Tuesday.

He is the highest-ranked statesman in Russia to be arrested since the failed coup in 1991.

The Investigative Committee, which directly reports to President Vladimir Putin, said the investigation would put forward charges soon.

“Ulyukayev was detained at night, immediately after interrogation,” an Investigative Committee official told Reuters.

It was not immediately clear, what exactly Ulyukayev, who has overseen massive government privatization, has been accused of.

Kremlin spokesman Dmitry Peskov told TASS news agency that “this is a serious accusation.”

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“In any case, only a court is able to decide anything,” he was quoted as saying.

Kremlin-controlled Rosneft bought 50 percent of Bashneft for 330 billion roubles ($5 billion) in October.