Russia’s Economy Minister Alexei Ulyukayev has been accused of taking a bribe to endorse a state takeover.
Russia’s main anti-corruption body, the Investigative Committee (SK), said he received a payment of $2m (£1.6m).
Mr Ulyukayev is the highest-ranking Russian official held since the 1991 coup attempt in what was then the USSR.
The SK said he had “threatened” to create obstacles for Rosneft’s operations when it took a 50% stake in another state oil company, Bashneft.
According to SK spokeswoman Svetlana Petrenko, “Ulyukayev was caught red-handed”, receiving a $2m bribe on 14 November for giving a favourable assessment of the Rosneft deal.
The apparent sting operation came after months of electronic surveillance, including phone-tapping, officials said.
The arrest was big news on Russia’s state-run TV channels, under the headline “Battle against corruption”.
If found guilty he could face a prison sentence of between eight and 15 years.
Mr Ulyukayev, 60, was appointed economy minister in 2013. An economic liberal in the 1990s, he became deputy chairman of Russia’s central bank in 2004.
A very strange privatisation
It was only in October that Rosneft, an oil giant controlled by the Russian government, bought 50% of Bashneft for 330bn roubles ($5bn). Bashneft itself was one of Russia’s largest state oil companies.
Russia is in the middle of an economic slump, largely because of the fall in crude oil prices, and had lined up several state companies for privatisation to replenish state coffers.
But the sell-off of Bashneft had been shelved in August, reportedly by the Kremlin because of a dispute over who would take it over.
The controversial privatisation returned to the agenda early last month, apparently because of the government’s need to raise money. Mr Ulyukayev promised last month that the entire sum paid by Rosneft would go to the Russian budget.
Economic liberals had fiercely opposed the idea of a state-owned company acquiring the government’s share in another state oil firm. It was seen as a victory for Rosneft’s chief executive, Igor Sechin, who has long been a close adviser to President Vladimir Putin.
The president said last month that he had been “rather surprised” by the government’s earlier position to delay the deal as Rosneft was “strictly speaking” not a state firm as part of it was owned by BP.
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”. Mikhail Leontyev told Russian TV later that “there cannot be any threat of cancelling the deal”.
Bashneft was itself taken over controversially by the Russian state when its owner Vladimir Yevtushenkov was arrested. Charges against him were later dropped.