Rakuten Inc. said Tuesday it will acquire major U.S. Internet advertising agency LinkShare Corp. for about $425 million (about 46.5 billion yen), a deal that will enable the Japanese online shopping mall operator to expand into the U.S. market.

The purchase, one of the largest ever by Rakuten, is expected to be completed within four to six weeks, with the expenses being fully covered by bank loans.

New York-based LinkShare runs a performance-based online advertising business called affiliate marketing.

Affiliate marketing is a rapidly growing business in the world advertising sector in which an ad firm places ads for clients on blogs and Web sites managed by individuals. When the ads lead to purchases of a product or services, the individuals receive compensation.

LinkShare has over 500 clients, including Apple Computer Inc. and Wal-Mart Stores Inc., and places ads on over 10 million blogs and other sites. It posted $32 million in sales in the year through June 2004.

LinkShare's senior management team, including Stephen Messer, chairman and chief executive officer, will continue running the company, Rakuten said.