President Donald Trump said on Sunday (Apr 12) the United States Navy would start blockading the Strait of Hormuz, raising the stakes after marathon talks with Iran failed to reach a deal to end the war, jeopardising a fragile two-week ceasefire.

The US Central Command (CENTCOM) said US forces would begin implementing the blockade of all maritime traffic entering and exiting Iranian ports at 10am ET (10pm, Singapore time) on Monday.

It 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," a CENTCOM statement on X said.

US forces would not impede freedom of navigation for vessels transiting the Strait of Hormuz to and from non-Iranian ports, and additional information would be provided to commercial mariners through a formal notice prior to the start of the blockade, it said.

Trump said in a post on social media that the US would take action against every vessel in international waters that had paid a toll to Iran, and begin destroying mines that he said the Iranians had dropped in the strait, a choke point for about 20 per cent of global energy supplies that Iran has blocked.

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

Iran's Revolutionary Guards responded to Trump by warning 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.

Iran's Parliamentary Speaker Mohammad Baqer Qalibaf, who led his country's delegation to the talks along with Foreign Minister Abbas Araqchi, said Trump's new threats would have no effect on Iran.

"If you fight, we will fight, and if you come forward with logic, we will deal with logic," he said in comments carried by state media.

The weekend talks in Islamabad, which followed the announcement of a ceasefire on Tuesday, were the first direct US-Iranian meeting in more than a decade and the highest-level discussions since the 1979 Islamic Revolution.