Donald Trump's former campaign manager Paul Manafort secretly paid former senior European politicians to lobby for Ukraine's previous pro-Russia government, a new indictment says.
It alleges the group was led by a former European chancellor; ex-Austrian Chancellor Alfred Gusenbauer has denied to the BBC that it was him.
The indictment has been brought as part of a US investigation into claims of Russia meddling in the US election.
Mr Manafort denies all the charges.
His former aide, and Mr Trump's ex-deputy campaign manager, Rick Gates, has admitted conspiracy and lying to investigators in a plea deal.
There are no allegations that either Mr Manafort or Mr Gates colluded with Russia to influence the outcome of the 2016 presidential election, which is the main thrust of US special counsel Robert Mueller's investigation.
What are the latest allegations against Mr Manafort?
Mr Manafort faces new charges of conspiracy, money-laundering, failing to register as an agent for a foreign actor and making false statements.
The charges relate to his work for Ukraine's pro-Russian Party of Regions and its leader Viktor Yanukovych, who was president from 2010 until he was overthrown and fled to Russia following anti-government protests in 2014.
Mr Manafort is said to have made tens of millions of dollars from an extensive lobbying campaign to bolster the Ukrainian government's reputation within Europe and the US. But, says the indictment, he failed to register his work as required by the law and hid the financial proceeds in off-shore accounts.
The indictment also details ways in which he allegedly tried to put distance between his lobbying work and its links with Mr Yanukovych.
One of those attempts was the creation of a body of ex-European politicians, informally called the Hapsburg Group, to whom he paid over €2m ($2.5m; £1.8m), the indictment says.
What do we know about the Hapsburg Group?
Mr Manafort "secretly retained a group of former senior European politicians to take positions favorable to Ukraine, including by lobbying in the United States", the indictment says.
It does not name the members of the Hapsburg group, but says the body was managed by a former European chancellor it calls "Foreign Politician A" in co-ordination with Mr Manafort.
The word chancellor is used in various government roles in Europe, but is the title for the head of government in Austria and Germany.
There has been speculation the former chancellor referred to in the indictment is Alfred Gusenbauer who was Austria's chancellor from 2007-08.
Mr Gusenbauer told the BBC that he had been part of "noble" efforts to bring Ukraine closer to the European Union, and admitted visiting members of the US Congress in 2013 about the issue.
He said he understood he was paid for his consultancy work by a US company - not by Mr Manafort, whom he met on two occasions, or Mr Yanukovych's government.
"I was not aware of the fact Mr Manafort was financing this activity and of course I was also not connected to his activities within the Ukraine," he said.
"I was not employed by Mr Yanukovych's government. I was, in the European, and American and general interest, working for an association agreement between Ukraine and Europe."
Former Italian Prime Minister Romano Prodi has also been linked in media reports to the group.
He told the BBC that he was part of a group of former European politicians who "tried to understand if something could be done, but nothing could be done. So we've stopped."
There is no suggestion that any of the European politicians could face further consequences as a result of their involvement in this case.
How many people has Mr Mueller charged?
Nineteen people - including Mr Manafort and Mr Gates - have been indicted by the special counsel:
- Michael Flynn, a former US national security adviser, pleaded guilty to lying to the FBI over meetings he had with the Russian Ambassador, Sergei Kislyak
- George Papadopoulos, a former Trump campaign adviser, admitted lying to the FBI about his contacts with Russians
- Last week, 13 Russians were charged with tampering in the 2016 US election and a California man, Richard Pinedo, admitted an identity theft charge
- This week London-based lawyer Alex van der Zwaan pleaded guilty in court to making false statements when questioned about his work for Ukraine's justice ministry
Mr Trump has said there was no collusion. Moscow has rejected US intelligence claims of interference.