Germany’s biggest bank is coming under pressure from a US senator to give further details of its lending to Donald Trump and meetings it has had with the administration.

Chris Van Hollen has written to Deutsche Bank asking for assurances that it will not use the president’s outstanding multimillion-dollar loans as “leverage”. The Democratic senator is also demanding to know whether the bank has restructured Trump’s debt or sold it to “foreign entities”.

Trump currently has two loans and two mortgages with Deutsche Bank and owes it about $340m (£270m). The bank has also extended another $950m to a venture in which Trump owns a 30% stake, the Wall Street Journal reported in January.

Van Hollen, who sits on the Senate banking committee, said he had “great concern” about possible conflicts of interest between Deutsche and Trump and questions about whether the bank’s role as the president’s largest creditor could influence multiple ongoing investigations into the German bank.

In a letter to Bill Woodley, the CEO of Deutsche Bank America, the senator wrote: “I am asking that you do not use your institution’s ties to President Trump as leverage in any of these ongoing cases or ongoing regulatory oversight.

“Further, I ask that Deutsche Bank and its executives do not take any actions to assist Mr Trump in circumventing any of his ethical obligations to avoid conflicts of interest.”

Deutsche Bank says its position is that it will not comment or guide on any stories about Trump’s financial affairs.

The letter, sent on Wednesday and obtained by the Guardian, comes as Deutsche Bank faces ongoing investigations by the Department of Justice into alleged money laundering involving Russia. It is also in settlement talks with federal officials over its alleged role in the mortgage crisis.

Van Hollen and another prominent Democrat, Congresswoman Maxine Waters, have raised concerns about whether Jeff Sessions, the US attorney general, could oversee an impartial investigation given the bank’s close ties to the White House. Van Hollen said Sessions had not responded to an earlier letter about his oversight of the Deutsche probes at the DoJ, but Van Hollen’s position on the banking committee means the German bank could feel compelled to reply.

In recent months Deutsche Bank’s alleged links with Russia have come under intense scrutiny. The FBI, meanwhile, has announced that it is investigating possible collusion in the run-up to the US election between officials from the Trump campaign and the Kremlin.

In January the New York Department of Financial Services (DFS) fined the bank $425m for failing to prevent $10bn of Russian money laundering. The “mirror trades” scheme was run out of its Moscow office. The UK’s Financial Conduct Authority imposed a £163m fine – its biggest ever – for the same offence.

The previous month Deutsche paid $7.2bn to settle a decade-old toxic bond mis-selling scandal with the US Department of Justice.

In March it emerged Deutsche played a prominent role in a second Russian money-laundering scandal. It was one of dozens of western financial institutions that processed at least $20bn – and possibly more – of criminal Russian cash. The scheme, “the Global Laundromat”, ran from 2010 to 2014.

The Guardian revealed in February that some of Trump’s immediate family members were clients of Deutsche, including the president’s daughter Ivanka, her husband, Jared Kushner, and Kushner’s mother, Seryl Stadtmauer.

In his letter Van Hollen said Kushner, the president’s trusted senior advisor, had a multimillion-dollar line of credit with the bank. Deutsche has provided $370m in financing for a Kushner Companies’ property in Time Square.

Deutsche has conducted a close internal examination of the US president’s personal account to gauge whether there are any suspicious connections to Russia. It was looking for evidence of whether loans to Trump, which were agreed in highly unusual circumstances, may have been underpinned by financial guarantees from Moscow. Sources inside Deutsche said no link was found.

But in his letter to Woodley, Van Hollen said he wanted more information about this internal review, triggered when Trump won the Republican nomination for president. The senator asked for a description of the bank’s “risk management” and whether any irregularities emerged during the internal inquiry.

Van Hollen is also seeking reassurances that the president and his family are not receiving preferential treatment in a way that would violate federal ethics laws, and further explanation of efforts to restructure Trump’s debt, including whether any had been sold to foreign entities.