The Sensex at the Bombay Stock Exchange dropped 206 points, or 1.2 percent, to 16,640, today, on concerns that the Reserve Bank may keep key policy interest rates unchanged at its policy review next week. The Nifty at the National Stock Exchange fell 67 points, or 1.3 percent, to 5,043.But stock markets in Japan, Hong Kong, South Korea and Singapore rose between 0.1 percent and 0.9 percent, on hopes for more US stimulus to support growth.