Extending its losses for the third straight session, the Sensex at the Bombay Stock Exchange fell 287 points, or 1.8 percent, to close below the key 16,000 level, at 15,865, today. The market fell on sustained selling by investors, amid continued weakness in global stock markets, and as Moody's Investor Service lowered State Bank of India's rating. The Sensex had lost almost 550 points in the past two trading sessions.The Nifty at the National Stock Exchange declined 77 points, or 1.6 percent, to 4,772. Stock markets in Japan, Hong Kong, South Korea and Singapore lost between 1 percent and 3.5 percent, amid growing concerns about Europe's debt troubles.