The US threatened Iran with what it called “the greatest financial offensive ever marshalled” as it prepared to impose new economic sanctions on Monday targeting Iran’s trade partners.

Iran, in response, vowed to halt all oil exports from the Gulf if the “economic war” continued.

US Treasury Secretary Scott Bessent is due to hold a press conference at 1 pm EDT (1700 GMT) on Monday, amid expectations that Washington will announce tougher measures against Iran, which has faced near-continuous economic sanctions since the 1979 Islamic Revolution.

“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 US and Iran have not exchanged military strikes for weeks, but neither side has engaged in meaningful talks to end the six-month-old conflict.

Thousands of people have been killed, mostly in Iran and Lebanon, since the US and Israel began strikes on February 28. The attacks have degraded much of Iran’s conventional military capacity and caused severe economic damage.

Iran, however, retains enough missile and drone capabilities to threaten its Gulf neighbours and oil tankers in the Strait of Hormuz, bringing shipping through the key waterway close to a standstill and putting pressure on global fuel prices. The status of Iran’s nuclear programme also remains unclear.

Without detailing the planned measures, Bessent warned countries that continue to engage with Iran’s economy and financial system that they could face consequences.

Iran has been preparing for the sanctions for days, issuing strong warnings of a possible military and economic response.

Mohsen Rezaei, secretary of Iran’s Supreme National Security Council, said on Sunday that Tehran could retaliate by halting oil exports from the Gulf.

“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 said 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.”

Bessent had previously urged China to cooperate with Washington, noting that China has historically sourced around half of its oil imports from the Gulf. China’s embassy in Washington said sanctions and pressure would not help resolve the conflict and called for diplomacy.

Iran’s economy was already under pressure from international sanctions before US and Israeli strikes damaged parts of its infrastructure.

Iranian officials have warned that further economic punishment could deepen hardship, trigger renewed unrest and further undermine the Islamic Republic’s legitimacy.

Iran entered the war with high inflation, a weakening currency, energy shortages, sanctions and deep structural weaknesses. It now faces damaged infrastructure, disrupted trade, lost production and the cost of reconstruction.

With no official face-to-face talks between the US and Iran since June, countries including Qatar, Pakistan and Turkey have sought to promote diplomacy.

Iran said Pakistan’s army chief, Asim Munir, would visit Tehran on Monday as part of efforts to restore peace and security in the region. A Pakistani government source said Munir would discuss recent developments, including the US threat of new sanctions.

US-Israeli strikes on Iran and Israeli attacks on Lebanon during the conflict have killed thousands and displaced millions, while the US has reported 18 military personnel killed and more than 750 wounded.