STORY: REPORTER: "Has the blockade started, sir?"

TRUMP: "Yeah, it started. Ten o'clock."

President Donald Trump said a U.S. military blockade of ships leaving Iran's ports had begun on Monday, as Tehran threatened to retaliate against its Gulf neighbors' ports after peace talks failed to end the conflict over the weekend. 

"If they don't agree there's no deal."

Outside the Oval Office, Trump said Iran had been in touch on Monday and wanted to make a deal but that he will not approve any agreement that allows Tehran to have a nuclear weapon.

"We're not going to let that happen."

Earlier, Trump warned that any Iranian "fast-attack" ship that goes near the U.S. maritime blockade would be  "eliminated."

U.S. Central Command said the blockade be "enforced impartially against vessels of all nations" entering or leaving Iranian ports in the Gulf and the Gulf of Oman.

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Two Iranian-linked tankers laden with oil products left the strait on Monday before the deadline, LSEG data shows.

An Iranian military spokesperson called any U.S. restrictions on international shipping "piracy."

:: File

NATO allies including Britain and France said they would not be drawn into the conflict by taking part in the blockade.

Instead, British Prime Minister Kier Starmer told parliament on Monday that he and French President Emmanuel Macron will convene a summit of leaders to (quote), "ensure freedom of navigation in the Strait of Hormuz."

"And let me be very clear: this is about safeguarding shipping and supporting freedom of navigation once the conflict ends."

Iranian political analyst Mohammad Ghaderi said the U.S. blockade will only lift energy prices again.

"Look, when the other side wants to reopen the Strait of Hormuz, logically surrounding it only adds another problem. But what is Trump's argument? His argument is that if Iran wants to prevent passage through the strait, then he will prevent Iran's passage in a much wider area. This does not solve America's problem. Yes, it imposes pressure on Iran, but it does not resolve America's problem. What does this mean? It means that the story of the escalating rise in energy prices will continue."

Trump announced the blockade after discussions in Islamabad between the sides over the weekend failed to reach a final agreement, including on lifting an Iranian threat to strike cargo ships transiting the Strait of Hormuz.

Those talks came after Tehran and Washington agreed last week to a two-week ceasefire. 

But on Sunday Washington said Tehran rejected its demands, and Iranian Foreign Minister Abbas Araqchi said they had encountered "maximalism, shifting goalposts, and blockade" from the United States at the talks.

Pakistani Prime Minister Shehbaz Sharif said efforts were still on to resolve the conflict.