Mumbai:The BSE benchmark Sensex dropped by 187 points to end at 17,187.34 on fresh selling pressure by operators and investors after global rating agency Standard & Poor's cut India's long-term credit rating outlook to negative from stable.

The 30-share index fell by 186.50 points, or 1.07 per cent, to finish the week at 17,187.34. The S&P CNX Nifty of NSE also fell by 81.85 points, or 1.55 per cent, to 5,209.00.

The Sensex dropped to week's low of 17,019.24 after S&P cut its outlook on India's long-term rating to negative from stable, citing a slowdown in investment and economic growth and a widening in the current account deficit.

The BSE Mid-Cap index declined by 2.27 per cent, while BSE Small-Cap index slipped by 2.53 per cent.

Key benchmark indices registered moderate losses in a lacklustre trading session on Thursday as traders rolled over positions in the derivatives segment from the near-month April 2012 series to May 2012 series.

However, the BSE-IT index shot up by 111.45 points, or 2.04 per cent.

India's largest software services exporter by revenues Tata Consultancy Services (TCS) jumped by 10.42 per cent to Rs 1,202.05 and was the top gainer from the Sensex pack. The stock rose after the management issued a positive future outlook at the time of announcement of Q4 results after trading hours on Monday.

Other gainers from the sensex pack were Reliance Ind (1.16 per cent), Icici bank (0.98 per cent), Sunpharma (0.80 per cent), ITC (0.59 per cent) and Maruti (0.45 per cent).

However, Gail India fell by 8.48 per cent followed by DLF 7.68 per cent, BHEL 6.79 per cent, Bajaj Auto 6.70 per cent, SBI 5.72 per cent, Larsen 5.57 per cent, Bharti Airtel 5.12 per cent, Wipro 4.24 per cent, Hindalco 4.16 per cent, Jindal Steel 3.89 per cent, Cipla 3.25 per cent, Coal India 3.09 per cent and Sterlite Ind 3.07 per cent.

 Among the major indices the BSE-Realty dropped by 5.39 per cent followed by the BSE-Capital Goods 4.83 per cent, the BSE-Power 4.52 per cent, the BSE-IPO 3.53 per cent, the BSE- PSU 2.84 per cent and the Bankex by 2.42 per cent.

The total turnover at BSE and NSE was Rs 11,061.34 crore and Rs 54,479.77 crore respectively as against the previous weekend's level of Rs 11,357.50 crore and Rs 52,825.53 crore.

Meanwhile, the stock exchanges conducted a special 1-1/2-hour trading session on Saturday, April 28, as the National Stock Exchange (NSE) was upgrading the capacity of its futures and options (F&O) trading system hardware and software to improve processing capability and handle increased activities in the market.