MUMBAI: The benchmark S&P BSE Sensex on Tuesday fell 651 points as the rupee once again breached the 68-mark to the dollar after a spate of negative news, including escalating tension in Syria.

Investors were spooked as Russian media said two missile launches were detected from the central Mediterranean Sea. The report came amid concern about military action in Syria.

Brokers said across-the-board selling was triggered by a report that Standard & Poor's had said chances of a credit rating downgrade for India were higher than for Indonesia.

After JP Morgan, HSBC Global Research and Nomura, Goldman Sachs today cut India's growth forecast for this fiscal to 4 per cent from 6 per cent earlier and said it expects the rupee to touch 72 against the dollar in the next six months.

The sensex, which started above the 19,000 mark, fell to close at 18,234.66, a decline of 651.47 points or 3.45 per cent. The drop was the most since August 16, when it fell 769 points or 3.97 per cent. It was the first loss after four sessions of gains, during which it added 918.05 points.

The series of negative news followed data on Friday that showed economic growth slowed to 4.4 per cent in April-June.

On Tuesday, the government said growth in eight infrastructure industries was 3.1 per cent in July, against 4.5 per cent a year earlier. An indicator of manufacturing sector activity in India contracted in August.

"The economy's fundamentals in the near term remain on shaky ground," said Vaibhav Agrawal, VP of research at Angel Broking. "Increase in oil prices due to the Syria situation is expected to add to the current account burden, keeping the rupee under pressure. As a result, hopes of quick reversal of interest rate hikes by the RBI are waning."

The nifty tumbled 209.30 points, or 3.77 per cent, to 5,341.45. The MCX-SX's SX-40 was down 3 per cent at 10842.41.

The rupee, which closed at 66 to the dollar yesterday, dipped to below the 68-mark in afternoon deals.

Banks, consumer durables and realty shares led sectoral indices lower. Reliance Industries lost 6.07 per cent and ITC fell 5.37 per cent, together contributing more than 220 points to the decline in the Sensex.

At close of trade today, shares of Tech Mahindra were up 1.81 per cent at Rs 1,399.70 on the BSE. During the day, shares of the company climbed 4.32 per cent to Rs 1,434.3 -- its 52-week high. On the NSE, the stock settled 1.73 per cent higher at Rs 1,398.90. In terms of volume, 2.15 lakh shares of the company changed hands on the BSE, while over 15 lakh shares were traded at the NSE. In the stock market, the BSE benchmark Sensex ended the day at 18,234.66, down 651.47 points.