SEOUL, South Korea — South Korean financial regulators on Friday said they were investigating whether nine executives from Samsung, the country’s largest conglomerate, used insider trading to profit illegally from a merger of two subsidiaries.

The country’s stock exchange reported the suspected insider trading, prompting the Financial Services Commission to investigate the Samsung executives, Kim Hong-sik, director of the commission’s capital markets investigation unit, told reporters on Friday.

Mr. Kim did not elaborate. But South Korean news media reported that nine executives from several Samsung companies bought 40 billion to 50 billion won, or $34.5 million to $43.1 million, worth of shares of a subsidiary, Cheil Industries, shortly before the plan to merge it with Samsung C&T was announced in May.

Cheil Industries shares rose sharply until the merger plan was announced on May 26.

“We understand the investigation involving certain individuals is still in its early stage,” Samsung said in a news release. “We will wait until the authorities conclude their investigation.”