US special counsel Robert Mueller has asked Germany's Deutsche Bank to provide records of accounts held by Donald Trump, according to reports.
Mr Mueller issued a subpoena to the bank several weeks ago demanding data on transactions linked to the US president, Reuters news agency and a German newspaper say.
Deutsche Bank has previously rejected similar requests from Democrats.
Mr Mueller is investigating claims of collusion between Mr Trump and Russia.
US investigators are said to be demanding information on dealings linked to Mr Trump as part of an investigation into alleged Russian influence in the US presidential election, according to Handelsblatt and Reuters.
Deutsche Bank, which is one of the Trump Organisation's major lenders on its real estate projects, said it would not comment on any of its clients.
In June, the German bank rejected requests for account records by Democrats in the US House of Representatives to provide details of the president's finances, citing privacy laws.
As special counsel Mr Mueller, who headed the FBI for more than a decade, has the powers to subpoena records and bring criminal charges.
He can also prosecute anyone who interferes in his investigation through crimes including perjury, obstruction of justice, destruction of evidence and intimidation of witnesses.
Mr Mueller's office has so far spent about $3.2m (£2.4m) on attorneys, special agents and other expenses as part of its investigation, the US Department of Justice revealed in a report on Tuesday.
US intelligence agencies have concluded that Moscow tried to sway the presidential election in favour of Mr Trump.
It is alleged that Russian hackers stole information linked to the campaign of his rival Hillary Clinton and passed it to Wikileaks so it could be released to undermine her.
Mr Trump has repeatedly denied any collusion with Russia, calling the allegations a "witch hunt".