Iran has promised to retaliate against expanded US economic sanctions, which Washington said would cut off Iran's economic lifeline.
Tehran has expressed confidence that major trading partners will resist the US pressure campaign.
US Treasury Secretary Scott Bessent unveiled the measures yesterday but stopped short of severe sanctions, saying countries that continued trading with Iran risked being forced out of the dollar-based financial system.
"Around the globe, our objective is to sever every economic lifeline that sustains this tyrannical regime until Tehran stands alone," Mr Bessent told a press conference.
Mr Bessent declined to identify the countries that would be targeted or reveal when those penalties would take effect, saying he would instead provide them time to comply with the new directive.
The Treasury Department did announce new sanctions on 60 individuals, entities and vessels, but the list did not include any of the Chinese financial institutions suspected of facilitating Iran's oil trade.
China said today that it would safeguard its interests after Washington laid out plans for the "economic asphyxiation" of its economic partner Iran.
China has advocated for a ceasefire, and insisted US sanctions will not resolve the conflict.
"Cooperation between China and Iran has always been conducted within the framework of international law and should not be interfered with or disrupted," foreign ministry spokesman Lin Jian said.
"China has already stated many times that it firmly opposes illegal unilateral sanctions ... China will take all necessary measures to firmly safeguard its own rights and interests," he added.
Iran and the United States signed an interim deal in June aimed at ending the war that began with U.S. and Israeli attacks on Iran, but the Islamabad memorandum, as it is known, quickly faltered.
Mediator Pakistan made "significant progress" in the latest talks with Tehran that focused on measures such as prevention of further escalation of the conflict and the reopening of the Strait of Hormuz, the Pakistani military said in a statement today.
"The Iranian president candidly shared his government's perspective and we had a very constructive exchange on the issues involved," Interior Minister Mohsin Naqvi, who accompanied army chief Asim Munir to Tehran, said on X.
Iran has not yet commented on the latest talks with Pakistan.
Before news of the latest sanctions, Iran threatened both a possible military response and further reduction in oil exports from the Gulf in retaliation for any US economic measures.
After they were unveiled, Iranian Economy Minister Ali Madanizadeh said, "We are fully prepared for the US sanctions."
He told state television: "Naturally, the enemies intend to launch an economic terrorist attack on us, but we also have our own tools and know how to play the game. Our defense is no longer so defensive; the enemies should wait for an attack."
Neither China nor Russia had "accepted" the US measures, he added, predicting that other countries would resist them.
Brigadier General Hossein Mohebbi, a spokesperson for Iran's Islamic Revolutionary Guard Corps, vowed heavy blows to US vital interests and energy chokepoints if Iran's infrastructure is threatened, according to local news reports.
Struggling to resolve an unpopular war that has pushed up energy prices, the administration of President Donald Trump appears to be counting on further economic pressure, even though Iran has spent decades under layers of US and international sanctions that have battered its economy but have not deterred its leadership.
Despite no major strikes by either side in weeks, the war shows little sign of reaching a diplomatic solution.
The United States is seeking new ways to end Iranian attacks on ships in the Gulf and, more recently via its allies, in the Red Sea.
Just two commodity vessels transited the key energy chokepoint of the Strait of Hormuz on Monday, for the lowest daily tally since early May, shipping data showed.
Before the conflict, the strait carried about a fifth of global flows of crude oil and liquefied natural gas.
Almost six months have passed since the US and Israel launched strikes on Iran. Thousands of people have died, most of them in Iran and Lebanon.
While the war has degraded much of Iran's conventional military capacity, inflicted economic pain and killed then-Supreme Leader Ayatollah Ali Khamenei, Iran has preserved enough missile and drone capability to attack Gulf neighbors and threaten oil tankers in the Strait of Hormuz.
The exact state of Iran's nuclear program, which the Americans and Israelis aim to wipe out, remains unknown.
Chinese oil trade
Oil prices steadied today, having fallen more than $2 (€1.71) a barrel a day earlier.
When questioned as to why he stopped short of imposing penalties on Iran and declined to identify the countries that would be targeted, Mr Bessent responded, "why would I want to blow up the global financial system"?
He said he wanted to give countries and companies time to sever ties.
Mr Bessent previously urged cooperation from China, the largest buyer of Iranian oil for several years, although the US blockade of Iran's ports, renewed in mid-July, has already cut Iranian oil flows to China.
Experts say Washington is wary of Chinese retaliation for any sanctions on its banks ahead of expected talks next month between Trump and Chinese President Xi Jinping, with any curbs on China's exports of critical minerals especially sensitive.
When asked if Chinese banks dealing with Iran could be targeted, Mr Bessent said "no one is above the reach of US sanctions".