The Sensex at the Bombay Stock Exchange stood 143 points, or 0.8 percent in negative territory, at 18,631 in afternoon trade, a short while ago. Earlier in the morning, the Sensex had opened with a loss of 131 points, or 0.7 per cent, at 18,644 on fresh selling by funds, amid falling regional bourses.Stock markets in Japan, Hong Kong, Singapore, Indonesia and South Korea had lost between 1 percent and 2.3 percent, today, on mounting concerns that the US Federal Reserve may start scaling back its huge monthly bond-buying plan. The stock index in China had plunged 5.3 percent, amid brewing worries about that country's banking sector.