The 30-share index fell for the fourth straight session to close at 18,884.19 points, down 123.91 points. The Sensex has tanked by 3.51 per cent or 686.25 points in the four sessions.
"Investors are apprehensive that the ongoing political uncertainty may derail reforms and in the process delay economic recovery," said Sanjeev Zarbade, Vice President- Private Client Group Research, Kotak Securities.
The 50-issue CNX Nifty of the NSE also ended below the 5,700-mark at a fresh two-week low of 5,694.40, down by 51.55 points, or 0.90 per cent, over previous close.
Today, five DMK ministers submitted their resignation to the Prime Minister, raising concerns over the fate of key reform bills like pension and insurance which are pending in Parliament.
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Second-line stocks were at the receiving end on heavy sell-off by retail investors ahead of expiry of derivatives contract on March 28 as the BSE and the NSE will remain closed on on March 27 and 29 on account of 'Holi' and 'Good Friday', respectively, brokers said.
In 30-BSE index components, 19 stocks declined. Gains in Infosys, Tata Consultancy Services, Hero MotoCorp, Hindustan Uniliver and ITC capped the losses to some extent.