US equity indexes traded lower after midday on Thursday as crude oil surged to its highest in about six months amid mounting concern that the United States is poised to attack Iran.

The Dow Jones Industrial Average dropped 0.7% to 49,329.9, the S&P 500 declined 0.5% to 6,848.3, and the Nasdaq Composite slipped 0.4% to 22,670.2.

Energy, industrials, and utilities led the gainers while financials and health care were among the decliners.

In the energy market, West Texas Intermediate crude oil futures jumped 2% to $66.51 a barrel, the highest since August.

"At the centre of market anxiety sits the Strait of Hormuz, one of the world's most critical oil transit chokepoints," Ole Hansen, head of commodity strategy at Saxo Bank, said in a note. "Roughly 19-20 million barrels per day of crude and refined products pass through the narrow waterway -- close to one-fifth of global liquids consumption."

The ICE US Dollar Index rose 0.2% to 97.89, the strongest level in about four weeks.

US Treasury yields were mixed-to-little-changed, with the two-year at 3.47% and the 10-year at 4.08%.