Iran's chief negotiator on Tuesday issued an ultimatum to the United States to accept the conditions in Tehran's 14-point proposal for peace in the Middle East war or face "failure".
The defiant message came after US President Donald Trump rejected the latest counteroffer from Iran and said that a fragile ceasefire in place since April 8 was on "life support".
But Mohammad Bagher Ghalibaf said Washington had to accept Tehran's "rights" if it wanted to end more than two months of conflict, as peace talks remain deadlocked after an initial round failed to produce a breakthrough last month.
"There is no alternative but to accept the rights of the Iranian people as laid out in the 14-point proposal. Any other approach will be completely inconclusive; nothing but one failure after another," said Ghalibaf in a post on X.
"The longer they drag their feet, the more American taxpayers will pay for it."
Iran has refused to back down in its war with Washington, with military officials warning they are prepared to respond to any renewed US attack.
It has choked traffic through the key Strait of Hormuz trade route, rattling global markets and giving it vital leverage, while the US has imposed its own naval blockade on Iranian ports.
Details of the latest US proposal remain limited, though media reports say it involves a one-page memorandum of understanding aimed at ending the fighting and establishing a framework for negotiations on Iran's nuclear programme.
Iran's foreign ministry said its response called for ending the war on all fronts, including Lebanon, halting the US naval blockade on Iranian ports and securing the release of Iranian assets frozen abroad under longstanding sanctions.
It did not elaborate on what Iran would offer in return.
On Tuesday, the spokesman for Iran's parliamentary national security commission said lawmakers would consider the possibility of enriching uranium to weapons-grade levels if conflict resumed.
"One of Iran's options in the event of another attack could be 90 percent enrichment. We will examine it in parliament," Ebrahim Rezaei wrote in a post on X.
Tehran possesses a significant stockpile of uranium enriched to 60 percent purity, with roughly 90 percent required for a nuclear weapon.
Iran's stockpile of highly enriched uranium remains a key sticking point in negotiations with the United States, which insists the material must be transferred out of the country.
Iran has so far refused to move its enriched uranium stockpile abroad and insists on its right to the peaceful use of nuclear energy, though it has said the level of enrichment remains "negotiable".
Trump warns truce on 'massive life support'
US President Donald Trump warned the ceasefire in the Middle East war was on "life support" Monday after rejecting the latest counteroffer from Iran, which said its military stood ready to respond to any act of aggression.
The president's angry reaction to Iran's position -- delivered in response to a US proposal -- sent oil prices soaring and dashed hopes that a deal could be quickly negotiated to reopen the Strait of Hormuz to commercial shipping.
After slamming the reply as "TOTALLY UNACCEPTABLE," Trump insisted the United States would see a "complete victory" over Iran, adding that the truce which has largely halted fighting in the Gulf for over a month was on its last legs.
"The ceasefire is on massive life support, where the doctor walks in and says, 'Sir, your loved one has approximately a one percent chance of living'," he told reporters on Monday.
Iranian parliamentary speaker Mohammad Bagher Ghalibaf, who served as chief negotiator in previous talks with Washington, said shortly afterwards that his country was prepared "for any eventuality."
"Our armed forces are ready to respond and to teach a lesson for any aggression," he wrote on X. "A bad strategy and bad decisions always lead to bad results -- the world already understands this."
The developments unnerved global energy markets already thrown into chaos by the war and the overlapping blockades imposed by Iran and the US in the Strait of Hormuz -- a vital conduit for oil and gas shipments.
"The energy supply shock that began in the first quarter is the largest the world has ever experienced," the CEO and president of Saudi oil giant Aramco, Amin Nasser, told investors.
"If the Strait of Hormuz opens today, it will still take months for the market to rebalance, and if its opening is delayed by a few more weeks, then normalisation will last into 2027."
- Hunger and starvation -
Aside from energy, the world also faces a shortage of fertiliser -- much of which comes from Gulf ports -- and hence food for tens of millions of people.
Jorge Moreira da Silva, executive director of the United Nations Office for Project Services (UNOPS), told AFP there were just a few weeks left to avert a potentially "massive humanitarian crisis."
"We may witness a crisis that will force 45 million more people into hunger and starvation."
Trump did not say what had offended him in Iran's response, but Tehran's foreign ministry said it had called for an end to the US naval blockade of its ports and to the war "across the region" -- implying a halt to Israel's strikes targeting Hezbollah in Lebanon.
Crucially, ministry spokesman Esmaeil Baqaei told reporters Iran demanded the "release of assets belonging to the Iranian people, which have for years been unjustly trapped in foreign banks."
This would be not just a return to the status quo before the US and Israel launched the war on February 28, but a victory in the Islamic republic's long-standing campaign against its economic isolation.
"We did not demand any concessions. The only thing we demanded was Iran's legitimate rights," Baqaei said.
An end to international sanctions would diminish Washington's leverage over Tehran as it tries to secure a lasting end to Iran's nuclear enrichment.
The US, Israel and their allies have long accused Iran of seeking atomic weapons, an accusation Tehran has repeatedly denied.
Israeli Prime Minister Benjamin Netanyahu has insisted the conflict would not end until Iran's nuclear facilities were destroyed.
The Wall Street Journal, citing people familiar with the matter, said Iran's counterproposal had included the possibility of diluting some of its highly enriched uranium, with the rest transferred to a third country.
- 'Restraint over' -
The lack of a path to a resolution has focused concern on the Strait of Hormuz, where Iran is restricting maritime traffic and setting up a payment mechanism to charge tolls for crossing ships.
US officials have stressed it would be "unacceptable" for Tehran to control the international waterway.
Trump told Fox News that he was considering reviving a short-lived US operation to guide oil tankers and other commercial ships through the Hormuz, but that he had not yet taken a final decision.
Saudi sources previously told AFP that Saudi Arabia had prohibited the US from using its airspace and bases for the operation the first time around, fearing "it would just escalate the situation and would not work."
Seeking to increase economic pressure on Iran, the United States issued sanctions against 12 individuals and entities that it said facilitated the sale and shipment of Iranian oil to China.
It listed three Iran-based individuals and nine companies -- based in Hong Kong and the United Arab Emirates -- as being subject to the new sanctions.
As part of its blockade, the US Navy has at times fired on ships to disable them, or boarded and diverted them.
In a social media post on Sunday, the spokesman for the Iranian parliament's national security commission warned Washington: "Our restraint is over as of today."
"Any attack on our vessels will trigger a strong and decisive Iranian response against American ships and bases," Ebrahim Rezaei said.
- US gas tax suspension -
Trump said he plans to suspend a federal gasoline tax as consumers cope with surging energy prices in the wake of the Iran war.
US federal taxes on gasoline amount to 18.4 cents per gallon on gasoline and 24.4 cents per gallon for diesel. Suspending the tax would require an act of Congress, where Trump's Republican party holds a razor-thin majority in both houses.
Iran hangs man for armed rebellion
Iran on Tuesday executed a man convicted of armed rebellion, the judiciary said, the latest in a wave of hangings since war broke out with Israel and the United States.
"The death sentence for Abdoljalil Shahbakhsh, son of Jalal, a trained member of the Ansar al-Furqan terrorist group, was carried out this morning," the judiciary's Mizan Online website said.
He had been charged with rebellion "through armed attacks on police headquarters and membership in the Ansar al-Furqan rebel group", the authorities added.