Extending its falling streak for the seventh straight session -- the longest losing streak since December 22 -- the 30-share index fell by 439.95 points, or 1.39 per cent, to settle at 31,159.81 as RIL, HDFC, HDFC Bank, ITC, SBI and L&T dropped.
This is the weakest closing since June 30 when it had settled at 30,921.61.
The broader NSE Nifty cracked below the key 9,800-mark. It had regained the key 9,900-mark at the outset, but failed to hold on to the crucial level and dipped below the 9800-mark to hit a low of 9,714.40.
The September futures and options contracts are set to expire tomorrow, which made participants wait and watch.
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Sentiments suffered another setback amid expectations of a rate hike by the US Federal Reserve later this year, accelerating the pace of outflows by foreign investors, offsetting unabated buying by DIIs, brokers said.
Escalating North Korean worries too continued to dampen trading sentiments.
In addition, the rupee quoting at over six-month low of 65.75 against the dollar in day trade too dented the sentiment further.