Kai Pfaffenbach/Reuters

FRANKFURT — After a raid at Deutsche Bank’s headquarters, the company disclosed Wednesday that two of its highest-ranking executives were a focus of a tax evasion investigation, dealing a fresh blow to the German institution’s already battered reputation.

German authorities are looking into whether bank employees conspired to avoid sales tax on the trading of carbon emission certificates. As part of that inquiry, prosecutors are trying to determine whether Jürgen Fitschen, the co-chief executive, and Stefan Krause, the chief financial officer, played a role in signing certain tax forms.

On Wednesday, about 500 police officers searched Deutsche Bank offices in Frankfurt, Düsseldorf and Berlin, as well as private homes. The police arrested five people, who were not identified. Those arrested did not include Mr. Fitschen or Mr. Krause.

Deutsche Bank said it was cooperating with the authorities but added that it had already revised the reporting of value-added tax in question. “Unlike the Public Prosecutor’s Office, Deutsche Bank is of the opinion that this correction took place in due time,” the bank said in a statement. It declined to comment further.

Top executives sign many documents, and it was not clear whether prosecutors believed that Mr. Fitschen and Mr. Krause were knowingly involved in an attempt to avoid taxes. Prosecutors could not be reached for comment late Wednesday.

The investigation only complicates the bank’s turnaround efforts.

Like its rivals, Deutsche Bank is struggling in the face of the European debt crisis, weak economic conditions and new regulation. The bank could be hit particularly hard by new rules taking effect in the coming years that require banks to increase the amount of capital they hold as a cushion against losses. Deutsche Bank has acknowledged that it needs to bolster its reserves.

At the same time, Mr. Fitschen and Anshu Jain, the other co-chief executive, have been trying to improve the bank’s image. In September, Mr. Fitschen and Mr. Jain announced a broad effort to raise ethical standards. Acknowledging that the bank had made mistakes, the executives promised to reduce risk, set more modest profit goals and reduce employee bonuses.

But those efforts have been stymied by a series of legal issues.

The bank is among the institutions under investigation by the authorities in the United States and Europe over the possible manipulation of crucial benchmarks, like the London interbank offered rate, or Libor. In May, Deutsche Bank agreed to pay $202 million to settle claims by the United States Department of Justice that a bank subsidiary had filed false information to qualify for federal mortgage insurance. The bank is also the target of multiple lawsuits in the United States related to its sales of securities linked to the mortgage market.

While bank executives appeared to be surprised by the raid on Wednesday, the underlying allegations had been known for several years.

Since 2005, the European Union has set allowances for energy producers, manufacturers and other companies that produce carbon dioxide and other gases. Companies that do not use all their allowances may sell them, a system intended to give the companies an incentive to reduce their emissions.

The European Commission has repeatedly made changes to the system that are intended to prevent abuses. In the past, traders have collected value-added tax from customers but failed to pass the money on to governments.

In October, the Süddeutsche Zeitung, a newspaper in Munich, reported that Deutsche Bank fired five traders in connection with irregularities in carbon trading. The bank has not denied the report.