The S&P banks index slipped nearly 1 percent. JPMorgan and Bank of America fell about 1.2 percent, while Goldman Sachs dropped 1.6 percent.
The U.S. 10-year yields were down at 2.762 percent after U.S. President Donald Trump declared that missiles "will be coming" and blasted Moscow for standing by Syrian President Bashar Assad.
Russia had earlier warned that any U.S. missiles fired at Syria over a suspected chemical weapons attack on a rebel enclave would be shot down.
"There is going to be broad-based weakness, although one sector that is likely to outperform will be anything tied to the energy space," said Michael James, managing director of equity trading at Wedbush Securities in Los Angeles.
Escalating tension in Syria lifted oil prices to its highest in more than three years.
At 9:43 a.m. ET, the Dow Jones Industrial Average was down 0.57 percent at 24,269.
The S&P 500 fell 0.40 percent to 2,646.3 and the Nasdaq Composite dropped 0.35 percent to 7,069.38.
On Tuesday, the main U.S. indexes closed up nearly 2 percent after Chinese President Xi Jinping tried to defuse trade tensions with the United States by promising to lower import tariffs.
"With Xi's comments yesterday calming some of the trade war concerns, some of that optimism is going away with the concerns over what the final outcome might be over U.S. involvement over Syria," James said.
Data showing a rise in U.S. core inflation for March – which was up 0.2 percent and matched February's increase rise – failed to boost yields as headline consumer prices fell for the first time in 10 months.
The Labor Department said its Consumer Price Index slipped 0.1 percent, the first and largest drop since May 2017. But the core CPI, which excludes the volatile food and energy components, rose 2.1 percent year-on-year in March, the largest advance since February 2017.
The Federal Reserve is set to release the minutes of its March meeting, when the U.S. central bank voted to raise interest rates.
Among stocks, Hilton Worldwide jumped 4 percent after the hotel operator's main shareholder HNA Tourism Group decided to sell its stake in the company.
Facebook Inc shares edged lower as Chief Executive Mark Zuckerberg started his second day of testimony before the U.S. Congress.
In the first hearing on Tuesday, Zuckerberg made no further promise to support new legislation or change how the social network does business.
Declining issues outnumbered advancers on the NYSE for a 1.28-to-1 ratio and on the Nasdaq, for a 1.47-to-1 ratio favoring decliners.