NEW YORK (Associated Press) - Berlin prosecutors confirmed Saturday that they are investigating allegations against the chief executive of Deutsche Bank regarding a loan to the Russian energy company Gazprom.

The bank says the claims are part of a revenge campaign by former media tycoon Leo Kirch.

The Berlin prosecutor's office is looking into the allegation, brought by a private individual, that CEO Josef Ackermann gave "improper advantage" to former deputy finance minister Caio Koch-Weser, spokesman Michael Grunwald said.

Koch-Weser in 2005 agreed to the government's guaranteeing a loan worth at least 1 billion euros to Gazprom from Deutsche Bank. Three months later, Koch-Weser was named vice chairman of the Deutsche Bank group _ a move widely questioned by opposition parties at the time.

Grunwald would not elaborate, but Deutsche Bank said the complaint was filed by Kirch, who is involved in a lawsuit against Deutsche Bank.

"We have full confidence in the work of the investigative authorities and assume that the investigation will quickly show the groundlessness of the accusations," said Christian Streckert, spokesman for Deutsche Bank.

Streckert said it was a "revenge campaign" by Kirch, who is suing Deutsche Bank AG for $1.85 billion over claims the bank's former CEO undermined his group's creditworthiness and contributed to its eventual bankruptcy by implying in a television interview in February 2002 that banks would not lend the group any more money.

Kirch's spokesman was not available for comment Saturday.