Erasing initial gains, the BSE Sensex fell 188 points at midsession today, due to profit booking sparked off by reports of Standard & Poor's downgrading India's rating outlook to negative. 

The Sensex, which had climbed to 17,249.61 at the outset, fell back to trade lower by 188.05 points to 17,019.24 at 1300 hrs, following steep fall in stocks of realty and IT sectors. 

Similarly, National Stock Exchange index Nifty lost 62 points to 5,160.65. Selling pressure emerged as S&P cut the country rating outlook to negative from stable.

It also warned of a downgrade in two years if there is no improvement in the fiscal situation and the political climate continues to worsen. The lowering of outlook from stable (BBB+) to negative (BBB-) is expected to make external commercial borrowings expensive for Indian Inc.