Rakuten Inc., controlled by billionaire Hiroshi Mikitani, said it has agreed to buy streaming video service provider Viki Inc. as the Internet retailer seeks to expand into new digital offerings.

The companies see opportunities for Viki to boost revenue by selling more advertising against its video content, they said in a statement Monday, without giving the value of the deal. Viki has offices in San Francisco, Singapore, Seoul and Tokyo.

Rakuten in the past five years has announced more than $1.6 billion worth of purchases, including stakes in social network operator Pinterest Inc. and digital book seller Kobo Inc., as part of its strategy to compete with rivals such as Amazon.com Inc. Mikitani, who is also the chief executive officer of Rakuten, said last October that the company aims to have 70 percent of sales transactions overseas by as early as 2020.