NSE has stepped up its surveillance. CNBC-TV18 has learnt from dealers that brokers have been advised not to take fresh positions in the market.

Further, they have been asked to cut down their long leverage positions. It is being linked with the mark to market margins, which get hit, when stock prices go beyond a point. That was one of the reasons why, there was a sharp fall of 400 points in the morning.

The negative FIIs numbers are also being held responsible for this fall. The provisional numbers suggest that FIIs have sold around Rs 812 crore. The sell off that has been seen is done largely by hedge funds. Large funds and domestic mutual funds are buying at lower levels.

Tuesday's crash is because of the squaring off of leveraged positions in F&O as well.

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