Japan's largest e-commerce firm Rakuten Inc (4755.T) said it was in talks to buy U.S. rebate site operator Ebates, a deal reportedly worth $950 million and the latest in a long line of overseas acquisitions.

Shares of Rakuten fell 4.4 percent in mid-morning trade, underperforming the benchmark Nikkei .N225, which was flat.

The company has been on a buying spree to reduce its reliance on the domestic market, which accounts for the lion's share of its revenues. High-profile acquisitions in recent years have included free messaging application Viber for $900 million, and Canadian e-book reader Kobo for $315 million.

Media reports have said the deal could be worth more than 100 billion yen ($950 million). Rakuten said in a statement it was in talks but that no final decision on the deal had been made yet.

Ebates operates websites offering rebates and coupons from retailers including Amazon.com and Best Buy.