Oil prices jumped again Wednesday, while the U.S. stock markets fell ahead of a Federal Reserve decision on what to do with interest rates.

The S&P 500 fell 0.4%. The Dow Jones Industrial Average was down 614 points, or 1.2%, as of 10 a.m. Eastern time, and the Nasdaq composite was 0.5% lower.

The action was stronger in the oil market, where the price of international benchmark Brent crude leaped 6.2% to $87.14 per barrel after fighting resumed in the war with Iran, raising concern about the global flow of oil. Iran launched a barrage of missiles at American forces in the Middle East, while the U.S. military partnered with Saudi Arabia to strike Tehran-backed militias in Iraq.

Brent oil’s price had swung as low as $72 early this month and as high as $102 last week on uncertainty over whether the U.S. and Iran might reach a deal to allow oil tankers to move freely again through the Strait of Hormuz, from Middle East producers to customers worldwide.

The swings have raised worries that inflation will reaccelerate, just when it had begun to slow more than economists expected. That, in turn, has traders uncertain about what the Federal Reserve will announce after its two-day meeting on interest rates concludes later in the day.

Traders are betting on a roughly 36% probability that the Fed will raise its main interest rate, which would be the first increase in three years. Higher rates can keep a lid on inflation, but they can also slow the economy and undercut prices for stocks and other investments.

Higher rates particularly hurt stocks seen as the most expensive, and scrutiny has already been rising on makers of computer chips and other winners of the frenzy around artificial-intelligence technology. The surges for their stock prices are backed by real growth, but it may not be sustainable if AI does not produce as much profit and productivity as hoped.