South Korea's tax agency has launched an investigation into the nation's top Internet portal operator NHN Corp for the first time since 2007, a company official said Monday.

The official said the probe is a regular tax investigation that occurs every four or five years but NHN's first tax probe in 2007 forced the company to pay 1.48 billion won (US$1.3 million) in additional taxes.

The 2007 tax probe was the first on NHN since it was founded in 1999.

Naver is NHN's flagship Web portal that features a vast array of content, including email service, news, online shopping, games, blogs, entertainment and stocks.

Tax agency officials could not be immediately reached for comment. (Yonhap News)