US Treasury Secretary Scott Bessent has threatened to impose "the toughest sanctions in history" on Iran.
Iran's economy is already under huge pressure from international sanctions, its infrastructure has been hit repeatedly and thousands of people have been killed in airstrikes on the Islamic Republic since the US and Israel launched attacks on February 28.
But Tehran remains defiant after nearly six months of war and has brought shipping to a virtual standstill in the Strait of Hormuz, refusing to allow unauthorised oil tankers to transit a waterway that is vital for global oil shipments.
The effective blockade of the strait has pushed up global oil prices.
Describing what he said were "repetitive scenarios", Iranian Foreign Minister Abbas Araqchi said in a video posted on Telegram: "The fact that they (US leaders) have moved on from military operations ... to bring up the same old plans shows that they are desperate."
He said Washington must speak to Iran respectfully to find "a solution based on justice and honour."
"We have never been afraid. All of their actions - whether blockades or other military moves they have made - have failed, and this new issue of theirs will fail as well," he said on Sunday.
US President Donald Trump has warned of economic consequences against any country that provides "any type of lifeline to Iran" and Bessent has urged co-operation with Washington by China, which buys more than 80 per cent of Iran's shipped oil, according to 2025 data from analytics firm Kpler. China has urged 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, but gave few details.
Pakistan has been mediating in the conflict and a Pakistani government source said Munir would touch on recent developments including the US threat of new sanctions.
Trump said on Friday that Washington was observing "what happens" in the conflict.
"They would love to make a deal, but they're not ready to make the right deal, in my opinion," Trump said of Iran.
US attacks have severely diminished Iran's economy and devastated its navy and air force, but Tehran maintains enough missile and drone capability to impede oil tanker traffic and attack regional rivals.
Trump has yet to achieve objectives he set at the start of the war such as dismantling Iran's nuclear program — the state of which remains uncertain given that UN inspectors have been shut out since 2025 — and creating conditions for Iranians to overthrow their clerical rulers.
While Iran remains defiant, President Masoud Pezeshkian has also called for a diplomatic solution.
"It would be better to end the war today, when we are powerful and have dignity, and the whole world acknowledges our victory and emphasises that America, contrary to all regulations, attacked our schools, hospitals, and infrastructure and is hated in the world," the ISNA news agency quoted him as saying on Friday.
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