President Donald Trump on Sunday ordered a US naval blockade of the Strait of Hormuz in response to Iran's "unyielding" refusal to give up its nuclear ambitions during failed peace talks in Islamabad.

While acknowledging that the marathon negotiations in Pakistan had gone "well" and "most points were agreed to," Trump said Tehran had refused to concede on the issue of its nuclear program.

"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 suggested that "other countries" would be involved in the blockade effort, without specifying.

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 -- the highest-level meeting between the two sides since the 1979 Islamic revolution.

Tehran's delegation also included Foreign Minister Abbas Araghchi.

The talks were meant to solidify a fragile two-week ceasefire with a final deal to end the conflict that has engulfed the Middle East, leaving thousands dead and roiling global markets. But no conclusions were reached.

"We leave here with a very simple proposal, a method of understanding that is our final and best offer. We'll see if the Iranians accept it," Vance told reporters.

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.

Trump slammed Iran for promising to open the Strait of Hormuz, a strategic waterway through which a fifth of the world's crude oil passes, and "knowingly" failing to deliver.

"They say they put mines in the water, even though all of their Navy, and most of their 'mine droppers,' have been completely blown up. They may have done so, but what ship owner would want to take the chance?" Trump said.

"As they promised, they better begin the process of getting this INTERNATIONAL WATERWAY OPEN AND FAST!"

Iran had effectively blocked the Strait of Hormuz for weeks, since the United States and Israel launched a bombing campaign against the Islamic republic more than six weeks ago.

On Saturday, the US military announced that two of its warships had transited the strait at the start of a mine clearance operation.

Trump warned that eventually, US forces would "finish up the little that is left of Iran" if necessary.

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