The securities regulator issued rules Tuesday to clamp down on executives selling shares of their publicly traded companies, trying to cool market speculation.

Company executives may not sell shares within one year of the initial public offerings or within six months of leaving their posts, the China Securities Regulatory Commission (CSRC) said in a statement on its Web site. The rules take effect immediately.

The government wants to curb speculation in the stock markets to break boom-bust cycles in a market that saw US$24.4 billion in stock offerings in the past year. The State Council, or Cabinet, approved a task force in February to crack down on illegal share sales and other banned activities.

The securities regulator and stock exchanges have been "paying close attention to and investigating share transfers'' that involve short-term speculation, according to a separate statement on the commission's Web site. There have been a few recent cases, the statement said, without providing further details.

This follows other measures introduced by regulators to dampen speculative buying since the beginning of the year.

Under the new rules, executives also may not sell annually more than 25 percent of their holdings, as measured by what they owned at the end of the previous year. The restriction doesn't apply to executives who have fewer than 1,000 shares.

Executives are defined as directors, members of the board of supervisors and other senior managers. Companies must report any changes in their management teams and the shares that they hold, according to the statement.