U.S. equity markets were halted Monday morning after the S&P 500 dropped 7 percent, as an oil price war between Saudi Arabia and Russia sent crude prices crashing.

The Dow Jones Industrial Average was lower by more than 1,800 points, or 7 percent, in the opening minutes of trading while the S&P 500 and Nasdaq Composite were down 7 percent and 6.86 percent, respectively. The steep slide caused the New York Federal Reserve to increase its daily cash injections into the banking system to $150 billion from $100 billion.

The stock-market selloff comes after a production dispute between OPEC members, led by Saudi Arabia, and Russia sent West Texas Intermediate crude oil, the U.S. benchmark, plunging by as much as 33.8 percent, the most since the outbreak of the 1991 Persian Gulf War, to a low of $27.34 a barrel in overnight trading. After a small rebound, WTI was trading down 23.3 percent at $31.65 a barrel.

Oil majors, including Exxon Mobil, Chevron and BP, were sharply lower, as were service providers Haliburton and Schlumberger. Read more at FOX Business