Germany's Commerzbank is negotiating a fine with US authorities of at least 500 million dollars over allegations it dealt with countries blacklisted by the US, such as Iran, the New York Times reported late Monday.
An agreement could be announced as early as this summer, the newspaper said, quoting what it called people briefed on the matter.
Shares in the bank plunged on Tuesday in afternoon trades on the Frankfurt stock exchange.
The Times said Commerzbank, Germany's second largest bank, is "suspected of transferring money through its American operations on behalf of companies in Iran and Sudan".
A settlement has only begun to be sketched out but it is expected to include at least 500 million dollars (365 million euros) in fines for Commerzbank, the Times said.
That would be a mere fraction of the 8.9 billion dollars (6.5 billion euros) that French bank BNP Paribas has agreed to pay over handling transactions that allegedly violated economic sanctions against Sudan, Cuba and Iran from 2002 to 2012.
Contacted by AFP, a Commerzbank spokeswoman declined comment on the report.
Commerzbank revealed in 2010 that its dollar transactions with Iran were under investigation in the United States. But it did not say what kind of fine it might end up having to pay.
The Times said a settlement with Commerzbank could set the stage for a separate settlement with Germany's largest bank, Deutsche Bank.
Deutsche Bank said last week it was cooperating with US authorities but did not at the time know where the probe might lead.
In Frankfurt, Commerzbank shares showed a loss of 5.40 percent to 10.87 euros, while Deutsche Bank was down by 2.01 percent at 25.57 euros in afternoon trades.
The DAX index of leading shares was 0.96 percent lower overall.