The Dow Jones Industrial Average and the broad-based S&P 500 index fell 0.1 percent, while the tech-heavy Nasdaq Composite Index lost 0.3 percent.
Futures prices for crude oil and gas rose sharply as there are no signs that the US and Iran can agree on a lasting end to the fighting.
Rising energy prices are increasing fears of interest rate hikes in the US. Later this week, a consumer price index will also be released, which could signal inflation and heighten interest rate fears.
Another sign of market unrest was that interest rates on US government bonds, regardless of maturity, rose sharply.
Semiconductor giant Nvidia is reportedly on the verge of finalizing a $500 billion AI financing package with other players. That didn't help Nvidia's stock, which fell 2.9 percent.
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