India's National Stock Exchange Ltd said on Friday it was investigating the block sales in two stocks, the latest in a series of unusual price movements to rattle the market.

"Religare Capital Markets Limited uses third party software for execution of orders on stock exchanges. Due to some technical issue in the software, unintended transactions got executed," the brokerage said in a statement.

"There was no broker error and no loss to any clients," it said, adding the matter was being looked into by the software provider. It said there was no impact on client business and the brokerage would operate normally on Monday.

A total of 2.07 million shares in Tata Motors were sold in six blocks at an average price of 274.92 rupees in the afternoon on Friday, well below the roughly 292 rupee level at which the shares were trading at the time.

Tata shares fell as low as 268.25 rupees before ending the session down 5.49 percent at 281.64 rupees.

Shares in UltraTech, a cement maker, ended down 3.4 percent after an earlier block sale of 41,863 shares took place at an average 1,853.80 rupees, also well below where shares were trading at the time.