Sergei Ignatyev, Russia's central bank chief, has said that nearly $50bn, or 2.5 percent of the national income, was sent abroad illegally in 2012, much of it controlled by a single group of people - whom he did not identify.
The study by the Bank of Russia appeared to amount to an indictment of lawlessness and corruption in the system of "Kremlin capitalism" that has taken hold under President Vladimir Putin.
The report found that more than half the flows involved firms linked to each other.
In a front-page interview, Ignatyev, who retires as bank chairman in June after 11 years largely free of controversy, told the Vedomosti newspaper: "You get the impression that they are all controlled by one well organised group of people,"
"With a serious concentration of efforts by law enforcement agencies, I think it is possible to find these people."
Ignatyev, 65, said that $14bn was part of illicit trade operations while the rest left Russia through "dubious" cash schemes.
"This could be payments for deliveries of drugs, [illegal] shipments, bribes and paybacks to officials ... or managers carrying out purchases in big private companies," Ignatyev said. "Or these could be tax avoidance schemes."
He called for urgent legislation that would allow banks to close down accounts being used for dubious purposes and also urged lawmakers to tighten rules for setting up companies.
Ignatyev was citing the findings of a study that the bank said it would publish later on Wednesday.
By lunchtime in Moscow, only Ignatyev's interview had been posted on the central bank's website (http://www.cbr.ru), not the study itself.
In a further indication of its sensitivity, Ignatyev did not touch on the subject of illegal capital flight in testimony on Wednesday morning to the Federation Council, the upper house of parliament. Neither was he asked about it by lawmakers.
Asked by a reporter before his testimony to identify the "well-organised group" he mentioned in the interview that was making half the illegal transfers abroad, Ignatyev declined comment and left the upper house without speaking to journalists.
The Kremlin also did not comment, beyond saying that it thought the figures were exaggerated, and there was no word from the wealthy businessmen known as "oligarchs" who struck it rich after the Soviet Union collapsed in 1991.
Anti-corruption activists say that capital flight can take any number of forms, with some banks shifting money through complex paper trails, shell companies and so-called "encashment" schemes designed to evade regulators.
Big state enterprises in particular are involved in shifting large sums of money abroad, sources say, while many of Russia's oligarchs use offshore centres to safeguard their businesses.
Statistics show that Cyprus is the largest source of foreign investment into Russia. Most of that money coming from the island is itself Russian in origin, bankers say.
The amount of dirty money flowing in and out of Russia has more than doubled over the past eight years, robbing the country of productive capital and driving a huge underground economy, a recent study by a US think tank found.
Global Financial Integrity, based in Washington, estimated that an average of $62bn in money earned from corruption, human trafficking, arms smuggling and other illegal activities has entered or left Russia each year since the start of 2004.