Lead image for US vows 'economic D-Day' as Iran threatens to halt all oil exports.
The US threatened Iran with what it called "the greatest financial offensive ever marshalled" as it prepared to roll out economic sanctions on Monday that target Iran's trade partners.
Iran in turn vowed to shut down all oil exports from the Gulf "if the economic war continues."
US Treasury Secretary Scott Bessent will hold a press conference at 1 pm EDT (1700 GMT) on Monday amid promises to reveal even more severe measures on a country that has endured near-continuous economic sanctions since the Islamic Revolution of 1979.
"At dawn begins an economic D-Day — the single greatest financial offensive ever marshalled against an adversary," Bessent wrote in an opinion piece published in the Financial Times on Sunday.
The warring nations have not conducted military strikes against each other for weeks, but they also have not engaged in meaningful talks to end the six-month-old conflict.
Thousands of people have died, most of them in Iran and Lebanon, since the US and Israel began strikes on February 28, degrading much of Iran's conventional military capacity and inflicting economic pain while killing Iranian Supreme Leader Ayatollah Ali Khamenei.
But Iran has preserved enough missile and drone capability to attack its Gulf neighbours and threaten oil tankers in the Strait of Hormuz, bringing shipping in the key waterway to a near standstill and pressuring world fuel prices. The exact state of Iran's nuclear program, which the Americans and Israelis aim to wipe out, remains unknown.
Without detailing specific measures, Bessent signalled the US would target "fearful nations" that practice "appeasement" by engaging with Iran's economy and financial system.