Citigroup Inc said on Sunday it has agreed to sell its stake in Japanese telemarketer Bellsystem24 to U.S. private equity firm Bain Capital for 93.5 billion yen ($1 billion).

Bain has been widely expected to buy Bellsystem24 after securing exclusive negotiation rights earlier this month.

Sources had told Reuters last week that Bain was close to finalizing a roughly 100 billion yen deal for the company, marking the largest buyout by a foreign private equity firm in Japan in nearly two years.

Bain has beaten off rivals Permira and a team of CVC Capital and Blackstone, which had also made offers in the final round of bidding for Bellsystem24.

Citigroup said in an e-mailed statement that it had agreed to sell its 93.5 percent stake in Bellsystem24 for 93.5 billion yen in cash in a tender offer to be launched by a firm owned by funds advised by Bain Capital.

The tender offer will likely start on or before November 20 and be completed on December 30, Citigroup said.

The U.S. bank said the deal was not expected to have a material impact on its net income or capital ratios.

Citigroup put Bellsystem24 up for sale as part of a global effort to raise cash and replenish its capital.

Citigroup has already sold broker Nikko Cordial, a fund management firm and a trust bank this year in Japan. Including the Bellsystem deal, it will have raised a total of about 964 billion yen ($10.8 billion), according to company press releases.

The sale of Bellsystem24 initially drew strong interest from a number of private equity firms including Kohlberg Kravis Roberts & Co, which teamed up with trading house Itochu Corp before dropping out of the race.

The Nikkei newspaper said the total cost of the deal for Bain would reach 120 billion yen, including a special dividend payment. No one at Bain Capital could be reached for comment.

The deal will rank as Japan's largest buyout by a foreign private equity firm since March 2008, when Permira bought agrichemical company Arysta LifeScience Corp for more than $2 billion.

Bellsystem24 is Japan's largest telemarketing firm. It competes against Moshi Moshi Hotline Inc and Transcosmos Inc in Japan.

Bellsystem24 is now owned by Citigroup Capital Partners, which was known as Nikko Principal Investments, a private equity arm of brokerage group Nikko Cordial, which was bought by Citigroup in 2007.

Nikko Principal paid 220 billion yen to buy Bellsystem24 in 2004. While the sale price is roughly half its purchase price, Citigroup has generated returns from its investment by restructuring the company's debt to take some cash out, a method known as recapitalization.

Bain's financing will be supported by banking units of Mitsubishi UFJ Financial Group Inc, Mizuho Financial Group Inc and Sumitomo Mitsui Financial Group Inc, sources familiar with matter have told Reuters.

(Reporting by Junko Fujita and Nathan Layne; Editing by Will Dunham)