The special counsel in the FBI's Russia inquiry Robert Mueller is now looking into President Donald Trump's business transactions as part of his ongoing probe - one of several - into alleged ties between the Trump 2016 election campaign team and Russians allegedly influencing the 2016 election, according to Bloomberg and The New York Times.

The Guardian newspaper also reported on Thursday that Deutsche Bank executives are expecting that the bank will soon be receiving subpoenas or other requests for information from Mueller, and that the special counsel's investigative team and the bank have "already established informal contact in connection to the federal investigation."

Mueller is reportedly investigating purchases by Russian buyers of Trump properties, the 2013 Miss Universe pageant in Moscow, a SoHo (New York) development involving Russian associates and Trump's 2008 sale of a Florida mansion to a Russian oligarch, Bloomberg reported.

"Those transactions are in my view well beyond the mandate of the special counsel," Trump's lawyer John Dowd said in a statement as reported by Bloomberg.

Trump said on Wednesday that Mueller would be "crossing a red line" if he expanded his investigation to look at Trump family finances beyond ties to Russia.

A long history

Deutsche Bank stepped in when few on Wall Street wanted to work with Trump in the 1980s and 1990s, and it is that relationship that has now come under scrutiny.

DB also has strong ties to Russia. It signed a "cooperation agreement" with Vnesheconombank, a Russian state-owned bank and a target of US economic sanctions, the New York Times reported.

Trump's advisor and son-in-law Jared Kushner met Vnesheconombank's chief executive, Sergei Gorkov last December. 

Federal US prosecutors also settled a case with a Cyprus investment vehicle, Prevezon Holdings, owned by a Russian businessman with connections to the Kremlin.

Prevezon Holdings was reportedly represented by Natalia Veselnitskaya, the Russian lawyer who met Donald Trump Jr. at another December meeting, apparently to offer damaging information about Trump's opponent in the presidential election Hillary Clinton.

Ivanka Trump is also said to be a Deutsche Bank client, as is Jared Kushner and his mother, who, the New York Times reported, have "an unsecured line of credit from Deutsche Bank, valued at up to $25 million."

DB - which has reportedly lent over $4 billion in loan commitments and potential bond offerings to Trump - rejected demands by Democratic lawmakers in the House of Representatives in June to provide details of Trump's finances, citing privacy laws.