The Kremlin has called on the US Treasury to come up with proof after it told a BBC investigation it considered President Vladimir Putin to be corrupt.
Spokesman Dmitry Peskov told reporters the allegation was an “official accusation” and a “total fabrication”.
Adam Szubin, who oversees US Treasury sanctions, told BBC Panorama that the US government had known Mr. Putin was corrupt for “many, many years”.
It is thought to be the first time the US has made such a direct accusation.
Washington has already imposed sanctions on Mr. Putin’s aides, but has stopped short of levelling corruption allegations at the president himself.
US restrictions were placed on a number of Kremlin insiders in 2014, after President Putin ordered the annexation of Crimea from Ukraine and conflict broke out in eastern Ukraine. The EU imposed similar measures against Russian companies and individuals, focusing on sectors of the Russian economy that were close to the elite.
The US government stated at the time that President Putin had secret investments in the energy sector.
Mr Peskov told reporters in Moscow that the Panorama allegations would have looked like “another classic case of irresponsible journalism, if not for an official comment from a representative of the US finance ministry”.
As such it was an official accusation. “It clearly shows who is directing this,” said Mr. Peskov, who added that such an allegation required proof, to show that the statements were not unfounded slander.
In the programme, Mr. Szubin spoke of how “we’ve seen [Mr Putin] enriching his friends, his close allies, and marginalising those who he doesn’t view as friends using state assets”, whether it concerned Russia’s energy wealth or state contracts. “To me, that is a picture of corruption,” he said.
US government officials have been reluctant to be interviewed about President Putin’s wealth, and Mr. Szubin would not comment on a secret CIA report from 2007 that estimated it at around $40bn (£28bn).
But he said the Russian president had been amassing secret wealth. “He supposedly draws a state salary of something like $110,000 a year. That is not an accurate statement of the man’s wealth, and he has long time training and practices in terms of how to mask his actual wealth.”
President Putin declined to be interviewed for Panorama but the Kremlin denies such allegations.