NEW YORK, Nov. 4 (Xinhua) -- Citigroup, the largest banking company in the United States, named former U.S. Treasury Secretary Robert Rubin as its new chairman Sunday, replacing Charles Prince who resigned over the company's billions of dollars in losses from investing in bad debt.

Prince, 57, announced his resignation in a company statement after Citigroup held an emergency meeting of its board.

Sir Win Bischoff, who runs Citigroup's European operations, was named acting chief executive.

"I am responsible for the conduct of our businesses," said Prince, who also served as Citigroup's CEO, in the statement. "Thesize of these charges makes stepping down the only honorable course for me to take as chief executive officer. This is what I advised the board."

In a separate statement, Citigroup said it would write down another 5 billion to 7 billion dollars after taxes, roughly three or four months of profit, for its 55 billion dollars of exposure to U.S. subprime mortgages.

The write-down equals 8 billion to 11 billion dollars before taxes, and may rise if markets worsen, the company said.

In the third quarter of this year, Citigroup took a hit of 6.5 billion dollars from asset write downs and other credit-related losses.

Rubin, 69, was given credit for much of the country's economic success in the 1990s as economic adviser to then president Bill Clinton and later Treasury chief.

In 1999, he joined Citigroup and chaired the bank's executive committee.

Prince, who became chief executive of Citigroup in October 2003, will continue to serve the company as an adviser while a permanent replacement is found.