South Korea's antitrust watchdog has launched an investigation into an online marketing and advertisement unit of NHN Corp. in what appears to be its stepped-up efforts to crack down on unfair business practices, industry sources said Tuesday.

The Fair Trade Commission (FTC) started to send a team of investigators on May 13 to the offices of the NHN Business Platform (NBP) located in Bundang, south of Seoul, to obtain related data and documents, according to the sources.

The investigators are reportedly from an FTC unit in charge of unfair business practices.

NBP develops online marketing products and engages in the search advertisement business. NHN, the operator of Naver, the country's most-visited Internet portal, has a 100 percent stake in the company.

Since global search advertisement operator Overture withdrew its business from Korea last year, NBP has been emerging as a powerful player in the sector apparently on the back of the market dominance of NHN.

The probe comes as the FTC launched its probe into NHN last week on suspicion that it might be abusing its market power in business transactions with smaller partners.

The probe is expected to be concentrated mostly on whether NHN and NBP have been involved in any actions that could hurt fair competition by using their business relations, market watchers said.

 "NHN is in charge of service development and other research efforts while NBP is the very unit that generates sales through its search advertisement business. So it is inevitable for the FTC to focus its probe on the NBP," said a source in the Internet portal industry on condition of anonymity. (Yonhap News)