South Korea's antitrust watchdog has launched an investigation into Kakao Corp., the operator of the country's most-used messenger service Kakao Talk, for possibly abusing its market leader position, industry sources said Thursday.

An investigation is underway into allegations that Kakao was involved in abusing its market dominance in deals with smaller service suppliers. A probe is also being conducted on its scheduled merger with Daum Corp., the country's No. 2 Internet portal operator, the sources close to the matter said on condition of anonymity.

Kakao is the operator of Kakao Talk, a messenger service that commands 37 million users in Korea, where the population stands at around 50 million.

On Wednesday, shareholders of Daum and Kakao approved the merger of the two firms that will create one of the biggest tech companies in Korea. (Yonhap)