Daniel Roland / AFP - Getty Images file

Deutsche Bank Chief Executive Josef Ackermann earns $12 million a year.

FRANKFURT, Germany - A suspicious envelope sent to Deutsche Bank Chief Executive Josef Ackermann - the face of capitalism in Germany - was a functioning letter bomb, investigators said Thursday.

German police told Reuters that a group calling itself the Informal Anarchist Federation had claimed responsibility for the package, which was intercepted late Wednesday.

It raised fears that a wave of protests against the failures and excesses of bankers could turn more violent, and prompted police across Europe to warn banks to be extra vigilant.

Deutsche Bank spokesman Klaus Winker said the bank alerted police immediately after the package came to the attention of mailroom workers during a routine screening.

The New York Police Department said it had been alerted to the scare late Wednesday, causing the department to dispatch patrols to the bank's offices in the city "solely as a precaution."

NYPD spokesman Paul Browne said the return address on the letter was the European Central Bank — the governing body for the 17-nation common European currency, which has its headquarters just across the park from Deutsche Bank in downtown Frankfurt.

Ackermann, 63, a Swiss who is the first non-German to head Germany's biggest bank, is one of the few senior managers in the country always surrounded by bodyguards. He is the highest-paid chief executive of a German blue-chip company, earning 9 million euros ($12 million) in 2010.

A previous Deutsche Bank head, Alfred Herrhausen, was murdered in 1989 by leftist Red Army Faction guerrillas who blew up his car.

"Initial investigations show that this was an operational letter bomb," the Criminal Investigations Office for the state of Hesse and Frankfurt prosecutors in a statement.

'Other ways of protesting'
Frankfurt's offshoot of the Occupy protest movement, which is critical of banks and has been staging protests in New York, Washington, London and many other cities, said it had nothing to do with the attempted attack.

"We condemn any action that is linked to violence," said Frank Stegmaier, an activist in the Occupy Frankfurt group, which has been camping outside the European Central Bank in the German financial capital since mid-October.

"Occupy has other ways of protesting," he added.

Security has been stepped up at Deutsche Bank offices around the world, banking sources said. One insider said the number of threats against Ackermann had increased in recent months and his security would be increased, although there were no plans to cancel public appearances.

Two Greek commercial banks said they had already been operating under top security conditions after similar letter bomb incidents last year.

One banking source said that since 2006 every item of mail sent to members of Deutsche Bank's executive committee was put through a security check.

European leaders were to meet in Brussels on Thursday and Friday to try to agree on a way out of a sovereign debt crisis that has triggered a wave of government austerity measures and caused Germans to fret they may have to foot the bill.

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Some experts said the euro zone debt crisis could have triggered the attempted attack.

"It seems likely the incident is linked to the groundswell of public anger toward the banking sector, as highlighted by a number of anti-capitalist protests around the world," said Louise Taggart, Europe and Eurasia analyst at AKE Group.

"A likely explanation is that the letter bomb was sent from Greece, which is facing a particularly difficult economic situation following the implementation of severe austerity measures," she said.

A letter bomb sent to Chancellor Angela Merkel last year originated in Greece and is thought to have been linked to an anarchist group in reaction to the extreme austerity measures.