SHANGHAI (REUTERS) - China's securities regulator said on Friday that it had restricted 24 stock trading accounts for suspected trading irregularities.

The accounts had been found to have abnormal bids for shares or bid cancellations and were thus suspected of affecting share prices or influencing investment decisions by other investors, the China Securities Regulatory Commission said in its official microblog weibo.

The regulator also said that it was investigating individuals and institutional investors who used computerised "programme trading" for causing recent volatility in the Shanghai and Shenzhen stock exchanges.

Automated or program trading is a type of trading in securities, usually consisting of a basket of stocks that are executed by a computer programme simultaneously based on predetermined conditions. CSRC said program trading amplifies gains and losses and increases market fluctuations.

China has taken a slew of steps to rescue its stock market after its 35-per cent plunge in less than four weeks since June 12, including clamping down on irregularities.

Shanghai shares fell 0.63 per cent in opening trade on Friday. The benchmark Shanghai Composite Index fell 23.34 points to 3,682.43. The Shenzhen Composite Index, which tracks stocks on China's second exchange, slipped 0.18 perc ent, or 3.83 points, to 2,124.33.