The talks in Islamabad, which ran from Saturday into early Sunday, were the first direct US-Iranian meeting in more than a decade and the highest-level discussions since Iran’s 1979 revolution.

The negotiations came days after a ceasefire began on Tuesday, aimed at ending six weeks of fighting that has killed thousands of people across the Gulf, throttled vital supplies of energy and sparked fears of a wider regional conflict.

The US Central ​Command said on Sunday that the US blockade, starting at 10am ET, would be “enforced impartially against vessels of all nations entering or departing Iranian ports and coastal ​areas, including all Iranian ports on the Arabian Gulf and Gulf of Oman.”

Vessels transiting the Strait of Hormuz to and from non-Iranian ports will ⁠not be impeded, the US military said.

Additional information would be provided to commercial mariners through a formal notice prior to the start of the blockade, it said.

President Donald Trump on ​Sunday also said US forces would intercept every vessel in international waters that had paid a toll to Iran.

“No one who pays an illegal toll will have safe passage on the high ​seas,” Trump wrote on social media, adding: “Any Iranian who fires at us, or at peaceful vessels, will be BLOWN TO HELL!”

He added that the US navy will begin destroying mines that the Iranians had dropped in the Strait of Hormuz, a choke point for about 20% of global energy supplies.

While shipping data showed three supertankers fully laden with oil passed through the Strait on Saturday, tankers were steering clear of the waterway on Monday, ahead ​of the US blockade.

Iran says ‘zero lesson learned’

After Trump’s initial remarks on Sunday, Iran’s Islamic Revolutionary Guards warned that military vessels approaching the strait will be considered a ceasefire breach and dealt with ​harshly and decisively, underlining the risk of a dangerous escalation.

A US official said Iran rejected Washington’s call for an end to all uranium enrichment, the dismantling of all major enrichment facilities and the transfer of ‌highly enriched ⁠uranium.

Iran also refused US demands that Iran cease funding for Hamas, Hezbollah and the Houthis, as well as fully open the Strait of Hormuz, the official added.

Iranian media said there was agreement on a number of issues, but the Strait of Hormuz and Iran’s nuclear programme were the main sticking points.

Iranian Foreign Minister Abbas Araghchi said Iran had “encountered maximalism, shifting goalposts, and blockade” when just inches away from an “Islamabad MoU.”

“Zero lessons learned,” he added. “Good will begets good will. Enmity begets enmity.”

Six weeks of fighting has killed thousands, roiled the global economy and sent oil prices soaring as Iran has prevented traffic through ​the Strait.

The US dollar and oil rose in ​early trading on Monday after the failure ⁠of the talks, while stocks in Asia eased.

Trump told Fox News’ Sunday Briefing programme that oil and gasoline prices may remain high through November’s midterm elections, a rare acknowledgement of the potential political fallout from the war.

Iran’s Qalibaf posted a map of Washington-area gasoline prices on social media with the ​comment: “Enjoy the current pump figures. With the so-called ‘blockade’. Soon you’ll be nostalgic for $4–$5 gas.”

More negotiations?

Trump told Fox News on Sunday that he believed ​Iran would continue to negotiate ⁠and called the Islamabad discussions “very friendly.”

“I do believe they’re going to come to the table on this, because nobody can be so stupid as to say, ‘We want nuclear weapons,’ and they have no cards,” he said.

But several hours later, the US president said he did not care whether a “desperate” Iran returned to the negotiating table.

“If they don’t come back, I’m fine,” Trump told journalists on Sunday night after ⁠he returned ​to the Washington area from an overnight stay in Florida.

Qalibaf blamed the US for not winning Tehran’s trust, despite ​his team offering forward-looking initiatives.

Iran’s President Masoud Pezeshkian, who discussed the talks in a call with Russian President Vladimir Putin, said Tehran wanted “a balanced and fair agreement.”

“If the United States returns to the framework of international law, reaching an ​agreement is not far off,” he told Putin, Iranian state media reported.