Wall Street opens mixed as Iran tensions test markets

The S&P 500 and the tech-heavy Nasdaq have slipped as investors weighed the potential fallout from a US pledge of an "economic D-Day" against Iran while awaiting AI giant Nvidia's results and a key inflation report later this week.

The moves mark a sober start to a pivotal week that may determine whether equities can shrug off a flare-up in Middle East tensions and worries tied to a tense bond market, which have interrupted their rally.

The US has said it could roll out economic sanctions targeting Iran's trade partners, in what it called "the greatest financial offensive ever".

Treasury Secretary Scott Bessent, who warned of an "economic D-Day" in an opinion piece published in the Financial Times, is scheduled to hold a press conference in the afternoon.

Concerns over surging energy prices and ballooning government debt had pushed US Treasury yields higher last week, with the 30-year yield touching a 19-year peak before the Treasury announced support measures.

Higher yields hammered growth-oriented technology stocks, causing Wall Street's three main indices to post losses last week.

Bessent could tap Treasury's near $US1 trillion ($A1.4 trillion) General Account to help fund bond buybacks, instead of issuing short-term bills, CNBC reported on Monday.

The 30-year US Treasury yield declined slightly but remained above the 5.0 per cent threshold.

The turbulence has sharpened focus on Federal Reserve chair Kevin Warsh's speech at the Jackson Hole symposium later this week, where investors will parse his remarks for clues on policymakers' reading of the Treasury's rescue efforts and the latest economic data.

Quarterly results from Nvidia, the world's most valuable company, are expected to be another key catalyst for markets.

Any sign of slowing growth could reignite concerns over stretched valuations and how far the AI-driven rally could run.

"Chips have become a frothy space. I just don't know what good news hasn't already been priced in," said Marta Norton, chief investment strategist at retirement and wealth services provider Empower.

"It doesn't necessarily mean that the fundamentals are challenged. You can have a great company but that doesn't necessarily make it a great investment at a given point in time."

While Apple and Amazon.com each gained less than a per cent, Nvidia lost 2.44 per cent.