At 10:15 am, the BSE S&P Sensex was down by 175 points at 37,210 while the Nifty 50 edged lower by 51 points to 11,025.
At the National Stock Exchange, sectoral indices were mixed with Nifty auto, financial service, media, metal, bank and realty in the negative zone. Nifty FMCG, IT and pharma showed marginal gains.
Among stocks, oil processing and marketing firms suffered the most as the United States blamed Iran for the weekend attack on Saudi Arabia's crude oil facilities.
Bharat Petroleum Corporation dropped by 6.1 per cent to trade at Rs 383.50 per share while IndiaOil Corporation was down by 3.3 per cent to Rs 125.80 apiece. Index heavyweight Reliance Industries slipped by 2.2 per cent.
The other prominent losers were Tata Motors, Mahindra & Mahindra, Yes Bank, State Bank of India, Bharti Infratel and Asian Paints.
However, those which traded in the green were Indiabulls Housing Finance, ONGC, GAIL, Sun Pharma and Dr Reddy.
Meanwhile, moves in Asian share markets were small with Japan shut for a public holiday. MSCI's broadest index of Asia Pacific shares outside Japan was a notch lower at 515.4 while South Korea's KOSPI was a tad higher by 0.4 per cent. Hong Kong's Hang Seng was down by 1 per cent.