2016A statue is seen next to the logo of Germany's Deutsche Bank in Frankfurt, Germany.

Deutsche Bank AG on Thursday said U.S. law prohibits it from responding to questions from U.S. lawmakers about President Donald Trump and his possible ties to Russia without a legally proper request because of regulations protecting customer information.

In a letter to five House Democrats, Germany's largest bank said U.S. federal privacy and confidentiality laws prevented it from sharing information on its reported banking relationship with the President and his family.

"We hope that you will understand Deutsche Bank's need to respect the boundaries that Congress and the courts have set in an effort to protect confidential information," lawyers for the bank from Akin Gump Strauss Hauer & Feld wrote in the letter.

Deutsche's correspondence follows a May 23 request from Maxine Waters, ranking Democrat on the House Financial Services Committee, and four peers, requesting information about the Republican president.

The original letter sought details that might show whether Trump's loans for his real-estate business were backed by the Russian government, including documents tied to any internal reviews of Trump's accounts at the bank.

The lawmakers initially gave Deutsche Bank until June 2 to respond, but the German lender requested more time.

The Democrats on their own cannot compel Deutsche Bank to hand over the information. The House committee has subpoena power, but Republican committee members, who make up the majority of the panel, would have to cooperate.

No Republicans signed the letter.

Public records show Deutsche Bank loaned Trump millions of dollars for real-estate ventures.

The letter was sent on a day Washington was consumed with testimony by former FBI director James Comey, who appeared before a Senate panel on Thursday and accused Trump of firing him to undermine an investigation into possible collusion between his 2016 presidential campaign team and Russia.

Moscow has denied the allegations of election meddling, and Trump has denied any collusion.

The congressional Democrats also sought information about a Russian "mirror trading" scheme that allowed $10 billion to flow out of Russia. In January, Deutsche Bank agreed to pay $630 million in fines over the scheme, which could have been used to launder money out of Russia.

The trades involved, for example, buying Russian stocks in roubles for a client and selling the identical value of a security for U.S. dollars for a related customer.Deutsche Bank provided the Democrats copies of settlements regarding the trades.