Advertising agency Dentsu Inc. said Tuesday it will buy a majority stake in U.S. data marketing agency Merkle Group Inc. as it expands its overseas portfolio.

Merkle Group has expertise in customer data analysis, with more than 650 major companies among its clients globally. It provides services such as market research and development of business strategy, Dentsu said.

Founded in 1971, Merkle Group posted sales of $436 million in 2015. It has about 3,400 employees in the U.S., Britain, Spain and China.

Dentsu plans to seal the deal in late September, with the investment amount undisclosed. The company will acquire the stake from the U.S. firm's shareholders through its global business headquarters Dentsu Aegis Network Ltd.