Citigroup Inc may fail to win full control of Japanese brokerage Nikko Cordial Corp with its 13.4 billion U.S. dollars bid as more shareholders hold out for a higher offer.

Investors controlling at least 28 percent of Nikko are seeking a better price, up from 21 percent two weeks ago. Citigroup raised its bid 26 percent to 1,700 yen (14 U.S. dollars) a share in March and has ruled out another increase, Bloomberg News said.

Failure to win more than two-thirds of Nikko's equity would leave the New York-based bank unable to exercise full power over actions such as mergers or the sale of a unit. That could force the U.S. bank to seek compromises over major decisions with investors who resisted its offer. The bid expires tomorrow.

"The freedom of management will be constrained," said Kenji Mizutani, professor of economics and business at Chukyo University in Nagoya. "Lack of absolute control may make it difficult for Citigroup to sell units to recoup some of its investment."

Orbis Investment Management Ltd, Nikko's second-largest investor, and other holders said they won't accept Citigroup's bid.