Days after some Democratic senators approached Deutsche Bank for details of US President Donald Trump's business deals, the bank has turned down the request citing legal and contractual boundaries, reports said on Saturday.

"We hope that you will understand Deutsche Bank's need to respect the legal, as well as contractual, boundaries that exist with respect to such confidential information," Deutsche Bank's law firm, Akin Gump, wrote in a letter dated April 21, seen by Reuters and Bloomberg.

The letter also said that "there is a critical legal distinction between inquiries conducted pursuant to congressional rules adopted by duly authorized committees, on the one hand, and informational requests made by individual members, on the other."

Democratic senators Richard Blumenthal, Sherrod Brown, Chris Van Hollen and Elizabeth Warren wrote to Christian Sewing, the chief executive officer of Deutsche Bank, requesting information about the bank's interaction with the president and his companies this year.

Read more: Deutsche Bank's 5 biggest scandals

In the initial letter, dated April 7, the senators wrote that there were "troubling new concerns about the extent to which Deutsche Bank holds financial leverage over the president," and if members of the Trump administration could offer "regulatory favors."

"It's outrageous we don't know what secret favors the President and his family might be getting from the bank, or what favors the bank may be getting in return," Senator Warren, once a candidate for president, said in a statement to Reuters, demanding answers to the senators' questions.

According to filings, Deutsche Bank is one of the largest creditors for the president's properties, which raised concerns that the bank may be offering the Trump family preferential treatment when it came to repaying loans amidst fallout over the coronavirus pandemic.

"The American people deserve answers and anything less is unacceptable," Senator Van Hollen said in a statement to Reuters, calling the bank's response "inadequate and unresponsive."

The bank is under investigation by the US Department of Justice. The US Supreme Court will hear arguments in a related case over whether the bank has to turn over the president's financial records subpoenaed by two congressional committees next month.

Every evening at 1830 UTC, DW's editors send out a selection of the day's hard news and quality feature journalism. Sign up to receive it directly here.