A person familiar with Mueller's investigation told the news agency Reuters on Tuesday that Germany's largest bank received a subpoena from the U.S. special counsel several weeks ago to provide information on certain money and credit transactions, confirming a report by German daily Handelsblatt published on the same day.
Mueller was appointed special counsel in May, after President Donald Trump fired Federal Bureau of Investigation director James Comey.
Mueller's investigators have, according to previous media reports, examined Russian purchases of Trump-owned apartments, the president's involvement with Russian associates in SoHo, and the president's 2008 sale of his Florida mansion to a Russian oligarch, Dmitry Rybolovlev.
Trump, his wife, daughter Ivanka and son-in-law Jared Kushner are understood to beclients of Deutsche Bank.
Bloomberg reported early on Tuesday that Deutsche Bank, the German bank that serves as Trump's biggest lender, had been forced to submit documents about its client relationship with the president after Mueller issued the bank with a subpoena for information.
In an interview this past July Trump told The New York Times that Mueller would cross a red line if he examined his or his family's finances.
Holding such debt, particularly if some of it was or is coming due, could potentially give Russian banks some leverage over Trump, especially if they are state-owned, said a second USA official familiar with Russian intelligence methods. "Look, this is about Russian Federation".
CNN Congressional Correspondent Manu Raju tweeted that Republicans on the House Intelligence Committee actually blocked the Trump finances subpoena, refusing to order Deutsche Bank to hand over the Trump Organization's financial records.
But some details are in the public domain: Mr Trump received a $106m loan from Deutsche Bank in 2011 to buy the Doral golf resort in Miami, according to the local land register. Law professor Ryan Goodman suggests that Mueller could be trying to determine if Trump's loans from the bank were guaranteed by Russian interests, which could mean he was indebted to them in ways that could compromise him.
Camera IconRobert Mueller has asked a German bank to look at account information of Donald Trump and his family.
Deutsche Bank, the largest bank in Germany, has lent the Trump organisation hundreds of millions of dollars for real estate deals. And he also has deep financial entanglements with alleged Russian oligarchs and mobsters.
Trump has consistently denied any collusion between his campaign and Russian Federation and has stated that he did not have any business dealings in Russian Federation.