12:28 PM EDT, 05/21/2026 (MT Newswires) -- US equity indexes fell, pressured by higher crude oil and Treasury yields, amid concern that Iran's nuclear ambitions could breach President Donald Trump's red lines.

The Nasdaq Composite fell by 0.5% to 26,136.5, with the S&P 500 down 0.4% to 7,404.4 and the Dow Jones Industrial Average lower by 0.2% to 49,888.2 in midday trading Thursday.

Iran's Supreme Leader Ayatollah Mojtaba Khamenei has ordered enriched uranium to remain in the Islamic Republic, Reuters reported Thursday, citing two senior sources from the country. On Wednesday, President Trump warned of resuming military action if Tehran does not provide "100% good answers" in negotiations facilitated by a trio of Gulf nations, CNBC reported.

Mediator Pakistan stepped up efforts to achieve progress in talks that Trump warned are on the "borderline" between a deal and renewed strikes, Al Jazeera reported.

Meanwhile, Iran is discussing with Oman how to set up some form of a permanent toll system that will formalize its control of maritime traffic through the Strait of Hormuz, Bloomberg reported.

West Texas Intermediate crude oil futures jumped 2.4% to $100.55, and Brent crude futures climbed 2% to $107.14 as Trump has previously said that Iran cannot have nuclear weapons and control Hormuz, the chokepoint to about a fifth of global crude oil flows.

US Treasury yields rose, with the 30-year up 2.2 basis points to 5.14%, heading back toward its highest since 2007, as higher crude oil prices can increase the challenge facing the Federal Reserve to tame inflationary pressures. The 10-year climbed 3.9 basis points to 4.61%, aiming to return to its strongest level in more than a year.