The Indian equity benchmarks extended losses on Monday on the back of negative global cues as escalating tensions between Ukraine and Russia kept investors on tenterhooks worldwide. The Sensex fell as much as 638 points and Nifty 50 index slipped below its important psychological level of 17,100. Meanwhile, Japan's Nikkei fell 0.7 per cent, Hong Kong's Hang Seng declined 0.55 per cent, Singapore Straits Times declined 0.05 per cent and South Korea's KOSPI slipped 0.53 per cent.