The securities watchdog has been probing the possibility of insider trading related to Livedoor Co.'s takeover of a used automobile dealer, sources said Saturday.

The share price of Jac Holdings Co. experienced sharp gains in abnormally large transactions on the second section of the Tokyo Stock Exchange on Aug. 25, before Livedoor announced after that day's trading that it intended to acquire the company, according to the sources.

The TSE reported its findings about the "unnatural" transactions to the Securities and Exchange Surveillance Commission, they said.