Prosecutors raid Commerzbank over 'cum-ex' tax fraud: report

German prosecutors on Tuesday raided the Frankfurt offices of Germany's second-biggest lender Commerzbank, media reported, looking for evidence of mass tax fraud known as "cum-ex".

"Investigative measures are being taken today related to the complex around cum-ex trading," Cologne prosecutors' spokesman Rene Seppi told AFP, declining to name the site or nature of the probe.

Business daily Handelsblatt had previously reported the raids targeted Commerzbank, citing "several people familiar with the matter".

A Commerzbank spokesman told AFP the firm "cannot comment on open investigations".

He added that "of course we are cooperating fully with the authorities."

"Cum-ex" saw investors quickly trade shares in companies back and forth around dividend day, allowing them to claim multiple rebates on a single dividend tax payment.

The Cologne investigators reportedly suspect that Commerzbank was involved in the scheme to defraud taxpayers, without itself directly pocketing such fraudulent tax rebates.

A trial began just last week against two British former investment bankers on 33 counts of tax evasion, accused of having deprived the state of at least 400 million euros ($440 million) of tax revenues from 2006 onwards.

The pair were employees of Unicredit subsidiary Hypovereinsbank.

Raids have also taken place at Commerzbank's crosstown rival Deutsche Bank, with several employees under investigation, while Clearstream was raided in late August.

And business lawyer Hanno Berger, believed to be the originator of the scheme, has been awaiting trial since May.

Germany changed the law in 2012 to close a loophole exploited by the practice.

A finance ministry spokesperson said last week that 2.4 billion euros worth of repayments had already been demanded after the ministry identified a total of 499 cases of suspected cum-ex fraud with a total damage of 5.5 billion euros.