Indian equity benchmarks the Sensex and Nifty fell sharply at the open on Monday after marathon US-Iran negotiations in Pakistan broke down without a deal, stoking fears of a prolonged conflict and driving crude oil prices higher. The two sides failed to agree during 21 hours of historic talks, casting doubt over a fragile two-week ceasefire, with each blaming the other for the collapse. All 30 Sensex-listed companies traded in the red in early trade, with Titan, Sun Pharma, and Bharti Airtel among the steepest fallers.