Washington DC - President Donald Trump on Sunday bafflingly ordered a US naval blockade of the Strait of Hormuz in the wake of failed talks with Iran over reopening the waterway.

In long and rambling social media posts, Trump first claimed that the marathon negotiations in Islamabad had gone "well" and "most points were agreed to."

But he said Tehran had been "unyielding" in its refusal to give up its nuclear ambitions, and had failed to open the strait, through which a fifth of the world's crude oil passes – a condition of the two-week ceasefire currently in place.

And he threatened China with a massive 50% tariff on its goods entering the US if it decides to lend Iran military support.

Politicians Graham Platner explains why he and his wife are seeking IVF treatment abroad

"Effective immediately, the United States Navy, the Finest in the World, will begin the process of BLOCKADING any and all Ships trying to enter, or leave, the Strait of Hormuz," Trump said on his Truth Social platform.

"Any Iranian who fires at us, or at peaceful vessels, will be BLOWN TO HELL!"

Trump initially suggested that "other countries" would be involved in the blockade effort, and then told Fox's Sunday Morning Futures with Maria Bartiromo that Britain "and a couple of other countries" would be sending minesweepers.

US Vice President JD Vance left Pakistan without a deal after weekend talks with a team led by Iran's parliamentary speaker Mohammad Bagher Ghalibaf.

Trump said he had been fully debriefed by the US negotiating team of Vance, special envoy Steve Witkoff and Jared Kushner, the president's son-in-law.

He slammed Iran for "knowingly" failing to deliver on a pledge to reopen the Strait of Hormuz, writing: "As they promised, they better begin the process of getting this INTERNATIONAL WATERWAY OPEN AND FAST!"

Iran has effectively blocked the strait for weeks, since the US and Israel launched an unprovoked bombing campaign against the Islamic republic more than six weeks ago.

On Saturday, the US military claimed that two of its warships had transited the strait at the start of a mine clearance operation, which Iranian officials quickly denied.

Trump also reiterated a threat to destroy Iranian power plants and other civilian energy infrastructure – a war crime – and warned that US forces would "finish up the little that is left of Iran" if necessary.

"We are fully 'LOCKED AND LOADED,'" he wrote.