A recently sanctioned Russian oligarch has been questioned by FBI agents over hundreds of thousands of dollars his company's US affiliate paid to Trump's longtime personal attorney.
CNN said Renova Group chairman Viktor Vekselberg was questioned along with his cousin Andrew Intrater, who heads the firm's US affiliate Columbus Nova, by agents investigating Russian interference in the 2016 American presidential election.
The payments were made after the election but while Michael Cohen was still Trump's personal attorney.
Vekselberg was among seven Kremlin-linked oligarchs the Trump administration slapped with sanctions in April.
The report came as Michael Avenatti, the attorney representing porn actress Stormy Daniels released a dossier alleging that Vekselberg and his cousin transferred "approximately $500,000" to Cohen in eight payments.
"Mr Cohen inexplicably accepted these payments while he was the personal attorney to the president," the document said.
Daniels, born as Stephanie Clifford, was paid $130,000 by Cohen as part of a non-disclosure agreement over an alleged affair with Trump.
She is suing Trump for defamation, and has also sought to be released from the non-disclosure agreement. Cohen insists Clifford has repeatedly violated the accord, but she argues it is invalid because Trump did not sign the document.
Special counsel Robert Mueller's team of investigators is probing whether Trump's campaign colluded with Russia in the 2016 election, and whether he illegally tried to obstruct the investigation.