Germany’s largest bank has failed to respond to a request from Democrats on a House of Representatives panel for details about Donald Trump’s possible ties to Russia, a Democratic staffer said on Sunday.

Several Democrats on the House financial services committee sent a letter last month to John Cryan, chief executive officer of Deutsche Bank, seeking details that might show if loans for Trump’s real estate business were backed by the Russian government.

The letter asked for details of internal reviews of Trump’s transactions and gave the prominent German bank until Friday to respond. The bank’s response did not address any of the questions posed in the letter and its Frankfurt headquarters declined to comment, as it has in the past.

“Deutsche Bank’s outside counsel has confirmed receipt of our 23 May 2017 letter but did not provide substantive responses to our requests,” a Democratic member of the staff told Reuters in an email on condition of anonymity.

The congressional inquiry is also seeking information about a Russian “mirror trading” scheme that allowed $10bn to flow out of Russia.

“Congress remains in the dark on whether loans Deutsche Bank made to President Trump were guaranteed by the Russian government or were in any way connected to Russia,” the Democrats wrote in their request to Deutsche Bank.

“It is critical that you provide this committee with the information necessary to assess the scope, findings and conclusions of your internal reviews.”

The Democrats cannot compel Deutsche Bank to hand over the information. The House committee has the power to subpoena the documents but Republican committee members – who make up the majority of the panel – would have to cooperate. No Republicans signed the document request.

Citing media reports, the Democrats called for the bank to hand over any documents tied to internal reviews of Trump’s personal accounts at the bank. They also said the bank should state publicly that it had reviewed both the “mirror trading” scheme and Trump’s accounts.

Mirror trading involved buying stocks, for example, in Moscow in rubles, with related parties selling the same stocks shortly thereafter through a bank’s London branch.

Trump is mired in controversy over FBI and congressional investigations into alleged Russian meddling in the 2016 presidential election and potential collusion between Moscow and the Trump campaign. Moscow has denied the allegations, and Trump has denied any collusion.