Bharti Airtel fell almost 5 per cent as telecom stocks dropped on concern Reliance Jio Infocomm's participation in the upcoming spectrum auction may hurt their market share and profitability.
Idea Cellular, Reliance Communications, Tata Teleservices, Tata Communications and MTNL dropped.
Tata Motors and Sun Pharma were among the 16 Sensex shares that declined.
Seven of the 12 BSE sectoral indices fell, led by auto, FMCG and healthcare stocks.
Some IT shares were in demand after HCL Technologies, the country's fourth-largest software services exporter, logged a 52-week high after posting a 58.4 per cent rise in profit.
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The index then dropped to end at 21,265.18, a fall of 24.31 points or 0.11 per cent. Yesterday, the Sensex had risen 256.61 points.
The CNX Nifty on the National Stock Exchange ended almost flat -- down two points to 6,318.90.
"Telecom stocks fell by 4 to 7 per cent...Global markets were flat to negative and also weakened market strength," said Rakesh Goyal, Senior Vice President at Bonanza Portfolio Ltd.