Phillips 66 jumped about 2.4 percent after Warren Buffett's Berkshire Hathaway disclosed late Friday a $4.48 billion, or roughly 10.8 percent, stake in the oil refiner.
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No major earnings were due on Wall Street Monday. The Chicago purchasing managers' index (PMI) for August came in at 54.4, slightly below expectations and last month's read, but still indicating expansion.
The U.S. dollar traded a touch lower against major world currencies, with the euro above $1.12 and the yen near 121 yen against the greenback.
Treasury yields came off session lows, with the 10-year Treasury yield near 2.21 percent and the 2-year higher near 0.73 percent.
The Dow Jones Industrial Average traded down 114.98 points, or 0.69 percent, at 16,528.03, with Merck the greatest decliner and Chevron the greatest advancer. The index ended August off 6.57 percent for its worst month since May 2010.
American Express was the only blue chip in the black for the month, while Walt Disney plunged 15.1 percent in August as the greatest decliner.
The S&P 500 closed down 16.69 points, or 0.84 percent, at 1,972.18, with health care leading nine sectors lower and energy the only advancing sector. In late-morning trade, index component Signet Jewelers hit an all-time high, while Sempra Energy and Exelon hit fresh 52-week lows.
All 10 sectors posted losses of 3 percent or more for the month, with health care the worst performer, off 8 percent. The index lost 6.26 percent for the month, its worst since May 2012.
The Nasdaq closed down 51.82 points, or 1.07 percent, at 51.82. The index is the only major average up for the year so far but lost 6.86 percent for the month, its worst since May 2012.
Apple closed down 0.5 percent on the day, off 7 percent for the month. The stock remains in correction territory.
The iShares Nasdaq Biotechnology ETF (IBB) plunged 3.25 percent on Monday, off 10.65 percent for August and in correction territory.
The CBOE Volatility Index (VIX), widely considered the best gauge of fear in the market, traded near 28. The VIX rose nearly 135 percent in August for its biggest monthly gain going back to 1990.
About three stocks declined for every two advancers on the New York Stock Exchange, with an exchange volume of 1.1 billion and a composite volume of about nearly 3.9 billion in the close.
Gold futures settled down $1.50 at $1,132.50 an ounce.
—CNBC's Gina Francolla and Giovanny Moreano contributed to this report.