Japanese online mall operator Rakuten said on Thursday it will acquire Buy.com Inc for $250 million, foraying into the U.S. market for the first time as it steps up its push to expand overseas.

This year Rakuten announced a joint venture with China's top search engine Baidu to launch a virtual shopping mall targeting the world's largest online population and has said it is also looking at opportunities to enter European and other markets.

California-based Buy.com had revenue of $62.5 million in 2009 and has a client base of about 14 million for its electronic commerce operations, Rakuten said in a statement.

Rakuten also runs operations in Taiwan and Thailand.

Rakuten, which also owns a stock brokerage, an online bank and a professional Japanese baseball team, had an operating profit of 56.6 billion yen ($617.6 million) in 2009, up 20 percent from a year earlier on revenue of 298 billion yen.

Prior to the announcement, Rakuten shares ended down 0.8 percent, in line with a fall in the Jasdaq market.

(Reporting by Taiga Uranaka; Editing by Edwina Gibbs)