Sumitomo Mitsui Financial Group <8316.T> said it would buy Citigroup's Japanese brokerage and key investment banking businesses for at least $5.6 billion in a deal that will reshape Tokyo's finance sector and create a banking powerhouse.

Sumitomo Mitsui, Japan's third-largest bank, said it would pay at least 545 billion yen ($5.6 billion) for retail brokerage Nikko Cordial Securities and Citigroup's stock and bond underwriting operations.

Citigroup said in a statement the total cash value of the deal was 774.5 billion yen ($7.9 billion).

Retail broking has been a weak point for Sumitomo Mitsui, which has lagged behind top banks Mitsubishi UFJ <8306.T> and Mizuho Financial Group <8411.T>, as well as leading brokerage Nomura Holdings <8604.T>.

Nomura last year bought Lehman Brothers' operations in Asia, Europe and the Middle East.

($1=97.50 Yen)

(Reporting by David Dolan; Editing by Rodney Joyce)