German investigators on Tuesday raided the Frankfurt offices of US bank Morgan Stanley in a probe related to "cum-ex" fraud schemes that cost European governments billions of euros in tax income, prosecutors said. 

The Cologne prosecutors office was "carrying out searches" at the offices of a bank in Frankfurt, it said in a statement.

Morgan Stanley confirmed to Bloomberg News that its premises were being searched.

As well as offices, investigators had "searched the private homes of two suspects", prosecutors said. 

The raids were related to "cum-ex transactions and related tax-evasion models" and aimed to secure "emails and written correspondence" related to the affair.

Several law enforcement agencies including "around 75 investigators from the Dortmund criminal police" took part in the operation.

First exposed in 2017, the "cum-ex" scam involved numerous participants swiftly exchanging company shares amongst themselves around dividend day, in order to claim multiple tax rebates on a single payout.

Used across Europe, the scheme is estimated to have left a multi-billion-euro hole in Germany's public finances. The Handelsblatt financial daily has put the figure as high as €30 billion.

In Germany, a change to the tax law in 2012 closed the loophole that enabled the practice.

Dozens of people have been indicted over the scandal in Germany, including bankers, stock traders, lawyers and financial consultants.

German lawyer Hanno Berger, the alleged mastermind behind the scandal, went on trial in Germany at the beginning of April.