ISLAMABAD — President Donald Trump on Sunday said the U.S. Navy would swiftly begin a blockade of ships entering or leaving the Strait of Hormuz, after U.S.-Iran ceasefire talks in Pakistan ended without an agreement.

U.S. Central Command announced that it will blockade all Iranian ports beginning Monday at 10 a.m. EDT, or 5:30 p.m. in Iran.

CENTCOM said the blockade will be “enforced impartially against vessels of all nations.” It said it would still allow ships traveling between non-Iranian ports to transit the Strait of Hormuz.

Trump wants to weaken Iran’s key leverage in the war after demanding that it reopen the strait to all global traffic on the waterway that was responsible for 20% of global oil shipping before fighting began.

Traffic in the Strait has been limited even in the days since the ceasefire. Marine trackers say over 40 commercial ships have crossed since the start of the ceasefire.

A U.S. blockade could further rattle global energy markets. “It’s going to be all or none, and that’s the way it is,” Trump told Fox News.

Trump said on social media that he told the Navy to “seek and interdict every vessel in International Waters that has paid a toll to Iran. No one who pays an illegal toll will have safe passage on the high seas.” He said other nations would be involved but did not name them.

Freedom of peaceful navigation is a basic principle of international maritime trade.

Iran says ‘if you fight, we will fight’

Iran’s Revolutionary Guard later said the strait remained under Iran’s “full control” and was open for non-military vessels, but military ones would get a “forceful response,” two semi-official Iranian news agencies reported.

During the 21-hour talks, the U.S. military said two destroyers had transited the strait ahead of mine-clearing work, a first since the war began. Iran denied it.

Trump’s plan to use the Navy to block the strait is unrealistic and he will have to concede on some issues with Iran, said Andreas Krieg, a senior lecturer in security studies at Kings College London. “There isn’t any tool in the toolbox in terms of the military lever that he could use to get his way,” Krieg said.

Trump said Tehran’s nuclear ambitions were at the core of the talks’ failure. In comments to Fox News, he again threatened to strike civilian infrastructure.

Parliament speaker Mohammad Bagher Qalibaf, who led Iran’s side, addressed Trump in a new statement on his return to Iran: “If you fight, we will fight.”

No word on what happens after ceasefire expires

The face-to-face talks that ended early Sunday were the highest-level negotiations between the longtime rivals since the 1979 Islamic Revolution.

Neither indicated what will happen after the ceasefire expires on April 22.

“We need to see an affirmative commitment that they will not seek a nuclear weapon,” said Vice President JD Vance, leading the U.S. side.

Iranian negotiators could not agree to all U.S. “red lines,” said a U.S. official who spoke on condition of anonymity because they were not authorized to describe positions on the record.