All three major U.S. stock indexes lost ground Thursday, weighed by technology shares, as Treasury yields rose on easing recession fears and global central bank officials convened at the Jackson Hole Economic Symposium.

Weakness in the so-called Magnificent Seven megacap growth stocks weighed heaviest on the tech-laden Nasdaq.

"There doesn't appear to be any kind of clear catalyst as to what's driving this sell-off," Scott Ladner, chief investment officer at Horizon Investments in Charlotte, North Carolina.

"People may be trying to square positions a little bit ahead of Nvidia (earnings) next week, or risk-out ahead of (U.S. Federal Reserve Chair Jerome) Powell's Jackson Hole speech tomorrow."

Central bank officials from around the world have gathered in Jackson Hole for the annual Economic Symposium. Investors will be laser focused on Powell's address on Friday for clues on the timing and extent of the Fed's policy easing cycle.

Powell is expected to assure the markets that the Fed will cut rates in September, Ladner said. "He'll be coy with the question about whether it's going to be a 25 or 50 basis point cut, but will probably try to lead the market towards 25."

"He will say he expects to start slow but will also emphasize that if they do see any further weakness in the labor market they can speed things up," Ladner added.

News of increasing U.S. jobless claims, following Wednesday's sharply lower benchmark payrolls revision, appear to confirm the labor market is less robust than expected and is gradually softening. This soothed recession fears while bolstering the case for a 25 basis point rate cut at the Fed's upcoming September policy meeting.

That sentiment was echoed in remarks on Thursday from Kansas City Fed President Frank Schmid, Boston Fed President Susan Collins, and Philadelphia Fed President Patrick Harker, all of whom indicated that a rate-cutting phase is shortly forthcoming.

"What Fed officials are saying is a rate cut is definitely on the table, but there's still time between now and September and data can move things," Martin said.

According to preliminary data, the S&P 500 lost 48.66 points, or 0.87%, to end at 5,572.19 points, while the Nasdaq Composite lost 299.63 points, or 1.67%, to 17,619.35. The Dow Jones Industrial Average fell 161.02 points, or 0.39%, to 40,729.47.

Among individual stocks, Snowflake raised its forecast for full-year product revenue. Even so, the data cloud analytics firm's shares slid as its margin forecast remained unchanged.

Shares of Zoom Video Communications jumped after raising its annual revenue forecast.

Advance Auto Parts tumbled after trimming its annual profit forecast.