Russian Economic Development Minister Alexey 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 arrested since 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 Russian TASS news agency that “this is a serious accusation.”

“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 rubles ($5 billion) last month. 

TASS reported Tuesday morning that the Russian Investigative Committee (IC) had confirmed “The minister has been detained.  Investigators plan to indict Alexey Ulyukayev and petition the measure of restraint soon.” 

"The circumstances of the crime are connected with Alexey Ulyukayev who holds a government post in the Russian Federation receiving $2 million on November 14 for the positive assessment provided by the Economic Development Ministry that allowed Rosneft to complete the deal on purchasing the government's 50 per cent stake in Bashneft," IC spokesperson Svetlana Petrenko said.

“The minister has been detained.  Investigators plan to indict Alexey Ulyukayev and petition the measure of restraint soon,” Petrenko added.  “The criminal case was opened based on Part 6 of Article 290 of the Russian Criminal Code, receiving a bribe in especially large amounts," she noted.

TASS reports that two sources familiar with the situation told it today that detention of Ulyukayev on suspicion of receiving a bribe for clearing the Rosneft-Bashneft deal does not cast doubt on the deal itself.

One source reportedly said, “The deal itself is not called into question.” 

Another source noted that the Bashneft deal and accusations against Ulyukayev are two different matters.  “No one says that selling the stake, that the privatization can somehow be reconsidered,” the second source said answering a question on whether charges against Ulyukayev call into question the deal itself.

If convicted, Ulyukayev faces a fine of up to 100 times the amount of the bribe and a ban on holding certain positions or engaging in certain activities.  Alternatively a jail term of eight to 15 years plus a fine of 70 times the amount of the bribe, or no fine, are also possible penalties.