Mumbai, Feb. 20 -- The military build-up in the Persian Gulf and a muddied US interest rate outlook dealt the biggest blow to Indian markets since the Union budget, with investors losing nearly Rs.6.8 trillion on Thursday. The benchmark Nifty plunged 1.4% to close at 25,454.35 while the Sensex shed 1.5% to 82,498.14. The broader market wasn't spared either-the Nifty Midcap 100 slumped 1.6%, while the Nifty Smallcap 250 fell 1.2%. Among Nifty's biggest laggards were IndiGo (-3.3%), UltraTech Cement (-2.9%), and Mahindra & Mahindra (-2.9%). The Wall Street Journal reported that the US has gathered the biggest air power in West Asia since the 2003 invasion of Iraq. A strike on Iran could trigger a spike in oil prices, as markets react to the p...