Wall Street's major indexes closed lower on Thursday as traders girded for a key speech by Federal Reserve Chair Jerome Powell the following morning, awaiting hints on where interest rates might be headed.

The Dow Jones Industrial Average dipped 0.3 percent to 44,785.50, while the broad-based S&P 500 Index slid 0.4 percent to 6,370.17. The tech-heavy Nasdaq Composite Index dropped 0.3 percent to 21,100.31.

There is "a general sense of caution" ahead of Powell's speech at the Jackson Hole Economic Policy Symposium, said Patrick O'Hare of Briefing.com.

While markets generally expect a 25 basis points rate cut at the Fed's next policy meeting in September, O'Hare warns that there could have been a slight "rethink about how certain" this outcome is.

He noted that some Fed officials have acknowledged they are not in a hurry to lower interest rates.

While recent employment data has been weaker than earlier estimates, inflation remains notably above the Fed's longer run two-percent target.

This underscores the delicate balance for Powell as he addresses the central bankers' conference on Friday morning.

Washington and Brussels released more details of their tariffs deal on Thursday as well, though O'Hare said the market shrugged these off.

On Thursday, traders also digested Walmart's earnings.

While the retailer reported revenue growth and raised its outlook for the fiscal year, it noted that tariffs have added to import costs.

Walmart shares closed 4.5 percent down. (AFP)