Media reports say the former campaign manager of Donald Trump is to face charges relating the Russia inquiry.
US media is claiming Paul Manafort was seen going into a office of the FBI in Washington on Monday, accompanied by his lawyer.
His former business associate, Rick Gates, has also been told to surrender to the federal authorities, according to news outlets.
Special Counsel Robert Mueller is investigating alleged Russian interference to swing the result of the 2016 presidential election.
The charges faced by Manafort are have been made clear in an indictment.
He faces 12 counts of various charges, including conspiracy against the United States, money laundering, and giving false statements.
The decision by the inquiry is a significant move to launch charges against a man formerly in Donald Trump's inner circle.
The US president fired his former campaign manager following reports of him having received a large sum of money from Viktor F. Yanukovych, a former president of Ukraine and pro-Russia politician.
It was revealed by The New York Times in July that Manafort and a number of other high-profile campaign executives had met with a lawyer believed to be affiliated with the Kremlin last year.
Donald Trump and his team have denied all allegations of collusion with the Russians, and the US President has labelled the scrutiny - which has overshadowed his first year in the position - as a "witch hunt" routinely on Twitter.