Russia’s Economy Minister Alexei Ulyukayev has been detained in connection with an alleged bribe.
Russia’s main anti-corruption body, the Investigative Committee, said Mr Ulyukayev received a payment of $2 million.
His ministry had given a positive assessment that led to the oil giant Rosneft acquiring a 50% stake in another oil company, Bashneft.
He is the highest-ranking Russian official to be detained since the 1991 coup attempt in what was then the USSR.
A spokesperson for the Investigative Committee, Svetlana Petrenko said, “This is about extortion of a bribe from Rosneft representatives accompanied by threats.”
“Ulyukayev was caught red-handed as he received a bribe,” Ms Petrenko said.
The Investigative Committee said the minister would soon be charged.
Rosneft, which is controlled by the Russian government, bought 50% of Bashneft for 330 billion roubles (($5 billion) in October.
A Rosneft spokesperson told the Tass news agency it acquired the Bashneft stake “in accordance with Russian law on the basis of the best commercial offer made to the operating bank.”
Mr Ulyukayev was appointed economy minister in 2013; prior to that, he had been deputy chairman of Russia’s central bank for a decade.