German Justice Minister Heiko Maas has warned banks that they could face legal action if they are not open about their finances and tax obligations in the wake of the so-called Panama Papers leak, which is said to implicate German banks and businesses.
"No one will be able to dodge the national rule of law and the German investigative authorities for long," Maas said at a conference in Berlin on Tuesday.
"Whoever is found to have been acting wrongly will be made to answer to a German court," he added.
The minister also suggested the creation of a so-called "transparency register" targeting firms that bank anonymously, but did not give further details on the proposed measure.
The leak of more than 11 million documents from Panamian law firm Mossack Fonseca, which details how money was funnelled to shell companies in tax havens, is said to call into question the finances of numerous politicians, sports stars and celebrities from across 80 countries.
Germany's Sueddeutsche Zeitung newspaper, the first media outlet to receive the documents, reported Tuesday that six of Germany's seven biggest credit institutions have opened or managed a total of 1,200 accounts for clients with the offshore service provider.
A total of 28 German banks are thought to do business via Mossack Fonseca accounts, according to the Sueddeutsche's assessment of the data.
"This secretiveness has to end," Maas told the Munich-based broadsheet.
Maas has vowed a tough response to owners of offshore bank accounts by tightening Germany's money laundering laws in a bid to tackle tax fraud and root out criminal financing.
It remains unclear whether the banks and businesses mentioned have been involved in illegal dealings. Mossack Fonseca has emphasized that it had never faced charges for criminal wrongdoing.
On Tuesday, the state prosecution service in Munich said it would launch investigations into accounts involving regional lender BayernLB and Germany's electronic engineering giant Siemens.
Attorney General Thomas Steinkraus-Koch said that it would look into whether there was any cause for suspicion of criminal wrongdoing by BayernLB.
The bank has also pledged to investigate its own Luxembourg-based subsidiary over its offshore activities.
The Federal Financial Supervisory Authority is considering investigations into a number of German banks, industry insiders said in Frankfurt on Tuesday.
"We can not allow a proportion of society to work hard, stick by the rules and pay taxes, while another proportion of society is intent to defraud," Vice Chancellor and Economic Minister Sigmar Gabriel told the Sueddeutsche in response to the fallout.
Finance Minister Wolfgang Schaeuble has said that the leaks could give momentum to the international fight against tax avoidance and anonymity. He has announced plans to present draft legislation on the matter by mid-April.
"We're taking control of the ball in this match and will carry the game forward," the minister's spokesman, Martin Jaeger, said on Monday in Berlin.
Jaeger added that the Panama Papers had come as no surprise to Schaeuble.
Last year, the banks HypoVereinsbank, HSH Nordbank and Commerzbank were fined millions of euros after it emerged that they had assisted clients in setting up bogus companies in tax havens like Panama so that they could avoid tax.
Germany's tax trade union said on Tuesday that offshore companies were almost always set up in an attempt to circumvent tax laws.
"In my view, there is no sensible, economic reason to set up an offshore account in a tax haven; unless you would like to defraud the treasury and avoid taxes," union chief Thomas Eigenthaler told broadcaster n-tv.
"In 99 per cent of cases, such a move serves tax avoidance, money laundering and fraud," he said.
In an interview with the Passauer Neue Presse on Tuesday, Eigenthaler said that the Panama leaks represented "merely the tip of the iceberg."