Tokyo, Japan (CNN) -- Japanese authorities are investigating possible insider trading, a Tokyo Stock Exchange spokesman said Friday.
Exchange spokesman Kazuhiko Yoshimatsu said "particular cases" were the focus of the investigation, but declined to provide details or specify which companies could be involved.
Yoshimatsu said the exchange and Japan's Securities and Exchange Surveillance Commission are examining an increase in short selling -- when investors sell borrowed stock, believing the price of the stock will fall and they can later buy it back at a lower price.
Short selling of certain companies' stock increased, he said, before those companies announced they would be issuing new shares.
"The TSE is concerned about allegations of insider trading and the impact on the confidence of investors, and, in turn, the markets," Yoshimatsu said. "We would like to maintain the confidence of traders in the Japanese market."