Citigroup said on Tuesday it would merge its retail securities business in Japan with unit Nikko Cordial Corp, as part of the U.S. financial firm's push in the world's second-largest economy.

Citigroup said last week it would buy out minority shareholders in Nikko Cordial, Japan's third-largest brokerage, for $4.6 billion. Under the buyout, Nikko Cordial will be delisted from the Tokyo exchange and Citigroup will list its own shares.

The two companies said in a statement they plan to bring their separate brokerage businesses together as early as May 2008.

While Citigroup's brokerage unit has just two outlets in Japan, Nikko boasts a network of 110 branches and strong recognition among domestic investors.

Under the integration the Citigroup unit, Citibank Securities, would likely be merged into Nikko Cordial, the companies said.

After more than 100 years as niche player in Japan, Citigroup has been steadily rebranding itself for the Japanese market.

Earlier this year the firm relaunched its Japanese unit as a local bank, becoming the first foreign bank to receive approval to operate as a local entity and making it easier to open new branches.

Citigroup is one of several financial firms, including London-based HSBC Holdings PLC, looking to target Japan's millions of wealthy individuals and the country's estimated $13 trillion in household assets.

Earlier this year Citigroup spent about $8 billion to buy a 68 percent stake in Nikko Cordial, its biggest-ever Asian acquisition.