Deutsche Bank's head office and other locations in Frankfurt were raided by 170 police officers and tax investigators on Thursday as part of a money laundering probe.
Prosecutors said the raids targeted two Deutsche Bank employees, and others who have not yet been identified.
The German bank is suspected of helping clients to set up offshore companies in tax havens, prosecutors said in a statement. Investigators are also looking at whether Deutsche Bank failed to report suspicious transactions.
Both the lender and prosecutors said the probe is related to the Panama Papers, a 2016 investigation into money laundering networks and shell companies set up by Panama-based law firm Mossack Fonseca.
Frankfurt prosecutors said that a subsidiary of Deutsche Bank in the British Virgin Islands had served more than 900 customers, doing €311 million ($353 million) worth of business in 2016 alone.
Deutsche Bank said it was cooperating with authorities and would release more details in due course.
"As far as we are concerned, we have already provided the authorities with all the relevant information regarding [the] Panama Papers," it said in a statement. "Of course, we will cooperate closely with the public prosecutor's office in Frankfurt, as it is in our interest as well to clarify the facts."
Germany's biggest bank employs roughly 95,000 workers and has assets worth €1.4 trillion ($1.6 trillion). It's one of 29 lenders designated by the Bank for International Settlements as playing a significant role in the global financial system.
The investigation is yet another headache for Deutsche Bank, which has struggled in recent years to turn a profit amid questions about its business strategy and direction, and the heavy financial burden of past misconduct.
The lender struck a $7.2 billion deal with the US government in January 2017 to settle claims that it packaged and sold toxic mortgages. It was fined $630 million the same month over a Russian money laundering scheme.
In September, Deutsche Bank was ordered by German regulators to tighten its controls to prevent money laundering and terrorist financing.
Shares in Deutsche Bank (DB) slumped more than 3% on Thursday. The stock has tumbled 47% so far this year.
Christian Sewing, a retail banking veteran who took over as CEO in April, has tried to accelerate an overhaul of the bank, which has already closed hundreds of branches, cut thousands of jobs and slashed costs.
A European problem
Danske Bank (DNKEY), the largest bank in Denmark, said in September that an internal investigation had uncovered a large number of suspicious accounts and transactions at its branch in Estonia.
Jimmy Gurulé, professor at Notre Dame Law School and former US Treasury official, said that stronger deterrents are needed.
"Even in the most egregious cases, banks are often only required to pay a monetary penalty for engaging in criminal activity, which is merely the cost of doing business," he said.