In the warning sent to a combined 2,151 companies listed on the country's benchmark KOSPI, the secondary KOSDAQ and the tertiary KONEX on Thursday last week, the Korea Exchange said it will keep closer tabs on company officials who engage in stock trading using nonpublic information, sources said.

The move came as some big name listed firms have been embroiled in insider trading accusations, with some of their officials pocketing a large sum of illegal profit.

Last year, employees of Hanmi Pharm Co., a leading pharmaceuticals firm here, were accused of "avoiding losses" by selling their stocks of the company after receiving the leak about a partnership between Hanmi and German drugmaker Boehringer Ingelheim. The South Korean financial regulators imposed fines totaling 2.4 billion won ($2.1 million) against the rule breakers.

Recently, the authorities launched an investigation into online game company NCsoft Corp. over possible insider trading that took advantage of undisclosed information.

According to data by the KRX, it detected 88 cases of alleged insider trading last year, followed by 57 market manipulations and 22 other illegal trade practices. (Yonhap)