Buy or sell stocks, Dec. 9 -- Indian stock markets tumbled on Monday after two straight sessions of gains, as investors booked profits amid persistent foreign fund selling. The sentiment also turned cautious ahead of this week's US Federal Reserve policy decision, prompting a defensive shift in markets.

The 30-share BSE Sensex slumped 609.68 points, or 0.71%, to close at 85,102.69, after plunging as much as 836.78 points (0.97%) to an intraday low of 84,875.59. The NSE Nifty 50 snapped its two-day winning run, falling 225.90 points, or 0.86%, to end at 25,960.55. During the session, it slipped 294.2 points (1.12%) to touch an intraday low of 25,892.25.

The BSE Midcap index slipped 1.73%, while the Smallcap index fell 2.20%, extending th...