US Treasury Secretary Scott Bessent said he would give details on Monday of the planned sanctions, after President Donald Trump warned of economic consequences against any country that provided "any type of lifeline to Iran."
The chief of staff of Iran's Armed Forces, Major General Ali Abdollahi, said the Islamic Republic's reaction would be broad and decisive.
"With preparedness across land, sea, air, air defence and cyberspace, Iran's armed forces will respond to the enemy's new threats with crushing, punishing and devastating responses," Abdollahi was quoted as saying by Iranian media.
Iranian leaders and Trump alike have issued triumphant and threatening statements even as each side has yet to prevail in the war that the US and Israel started nearly six months ago, killing thousands of people while drawing in other Gulf nations and pushing up global fuel prices.
US attacks have severely diminished Iran's economy and its conventional forces, but Tehran maintains enough missile and drone capability to impede oil tanker traffic in the Strait of Hormuz and attack regional rivals.
Trump, meanwhile, has yet to achieve objectives he set at the start of the war such as dismantling Iran's nuclear program and creating conditions for Iranians to overthrow their clerical rulers. The war has driven up gas prices and weighed heavily on his popularity, which fell to the lowest point in his current term in a Reuters/Ipsos poll this week.
Iran's parliament speaker, Mohammad Baqer Qalibaf, the country's main negotiator in mediated talks with the US, said Washington appeared to have concluded it could not prevail in its direct military confrontation.
"We must make plans to deal with the unjust sanctions so that we can overcome them," he said in neighbouring Iraq.
But, speaking to Iranian and Iraqi businesspeople late on Thursday, Qalibaf acknowledged the strain on Iran's economy.
"No matter how much military power we have, we won't survive if people are hungry and we don't have financial turnover, economic growth and national production," Qalibaf said, according to official news agency IRNA.
Iran has weathered near-continuous economic sanctions for nearly 50 years, since the Islamic Revolution of 1979, but its people are suffering high inflation, a weakening currency and energy shortages along with damaged infrastructure. Tighter sanctions could have wider international implications.
China buys more than 80 per cent of Iran's shipped oil, according to 2025 data from analytics firm Kpler, but further US economic warfare with Beijing, which has eased earlier restrictions on exports of its vital rare-earth minerals, risks retaliation.
China's embassy in Washington said, "Sanctions and pressure do not help resolve the problem" and called for diplomacy.
There are other risks, especially to US allies in the Gulf, some of whose energy facilities and the desalination plants they depend on for drinking water have come under Iranian attack.
The US and Iran have twice announced ceasefire deals, in April and June, aiming to restore the free flow of ships through Hormuz, which before February carried about a fifth of all traded oil. Iran and Oman, which lies just across the narrow strait, have been in separate talks with a stated purpose to resume navigation, but the US has opposed any deal that would impose a toll on ships.
