US vows 'economic D-Day' as Iran threatens to halt Gulf 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.

The US Treasury is expected to broaden the scope of secondary sanctions on entities and countries that maintain business ties with Iran, a source familiar with the plans told Reuters on Monday.

The move is aimed at giving countries a final warning to sever their business ties with Iran as Washington seeks to increase economic pressure on Tehran.

The source said Treasury Secretary Scott Bessent would also make clear that countries continuing to do business with Iran could risk having key companies and entities cut off from the dollar-based financial system.

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 2 p.m.

EDT (1800 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.

Without detailing specific measures, the US treasury secretary signaled the US would target "fearful nations" that practice "appeasement" by engaging with Iran's economy and financial system.

"They would do well to consider the consequences of sustaining it," Bessent wrote in the Financial Times.

A defiant Iran Iran has been bracing for the sanctions for days, issuing a series of strongly worded statements ​suggesting it planned a major military response.

Mohsen Rezaei, secretary of Iran's Supreme National Security Council, on Sunday suggested economic retaliation.

"If the economic war continues, not a single drop of ‌oil will be exported, neither through the Strait of Hormuz nor from anywhere in the Persian Gulf," Rezaei wrote in a social media post.

"Iran will regard any country's participation in or support for America's economic war against the Iranian people as an act of war." Iranian Foreign Minister Abbas Araqchi dismissed the threat of new US sanctions ​as a sign of desperation on Sunday and said the expected new measures would fail to defeat Tehran.

"The fact that they (US leaders) have moved on from military operations to bring up the same old plans (economic sanctions) shows that they are desperate," Araqchi said in a post on Telegram.