US military will begin a blockade of the Strait of Hormuz at 10 a.m. ET Monday, targeting vessels entering or leaving Iranian ports.
Negotiations in Pakistan led by Vice President JD Vance failed, with Iran refusing US demands to halt nuclear weapons development.
Trump announced the blockade, saying Iran broke its promise to reopen Hormuz, a channel that carries about 20% of global oil.
Oil prices rose above $100 per barrel and global equities wavered as markets reacted cautiously to the escalation.