Citigroup Inc. launched a tender offer for scandal-tainted Nikko Cordial Corp. on Thursday, a spokeswoman for the U.S. bank said, two days after raising the bid 26 percent to dispel shareholder opposition.

Citigroup, which owned 4.9 percent of Japan's third-largest brokerage at the end of 2006, will bid for the remaining shares through April 26 in a deal worth up to $13.35 billion, the bank said in a statement.

Citigroup initiated the offer for Nikko Cordial on the Tokyo Stock Exchange, said Mika Nemoto, a spokeswoman for the company's Japan unit.

If the bid succeeds, it will become the biggest foreign acquisition of a Japanese securities house. Nikko is expected to help Citigroup bolster its ability to sell mutual funds and other services in the world's second-largest economy.

On Tuesday, the boards of the two companies agreed to raise the offer price for Nikko Cordial 26 percent to 1,700 yen a share after its largest shareholders rejected the initial price of 1,350 yen as too low.

Douglas Peterson, head of Citigroup's Japanese operations, said Wednesday the bank would not raise the offer further, calling the bid price "fair and firm."

A surprising decision by the Tokyo Stock Exchange to keep Nikko Cordial's shares listed despite accounting fraud also played a factor.