The US has intercepted an Iranian-flagged cargo ship in the Gulf as part of its naval blockade, Donald Trump has said.

The US president wrote on his Truth Social platform that the Touska was seized by the US Navy after failing to respond to a warning to stop. Iran said it was a violation of the ceasefire and it would retaliate soon for the “act of armed piracy”.

The announcement came after the White House confirmed US Vice-President JD Vance would lead another delegation for a second round of talks on ending the war with Iran in Pakistan.

Tehran has not yet confirmed its attendance. Iranian state media has reported that officials will not participate while the US blockade remains in place.

“Today, an Iranian-flagged cargo ship named TOUSKA, nearly 900 feet long and weighing almost as much as an aircraft carrier, tried to get past our Naval Blockade, and it did not go well for them,” Trump wrote.

He added that the US had given the vessel fair warning to stop, which was ignored, “so our Navy ship stopped them right in their tracks by blowing a hole in the engineroom”.

“The TOUSKA is under US Treasury Sanctions because of their prior history of illegal activity. We have full custody of the ship, and are seeing what’s on board!”

US Central Command later released footage it said showed a naval vessel intercepting a cargo ship. In the footage, a gun can be seen firing in the direction of the cargo ship.

According to a statement carried on state media outlets, a spokesperson for Iran’s top military headquarters, Khatam al-Anbiya, said the US in “violation of the ceasefire opened fire on one of Iran’s commercial vessels in the waters of the Sea of Oman, disabled its navigation system, and boarded it” by “deploying” marines.

“Armed Forces of the Islamic Republic of Iran will soon respond to and retaliate for this act of armed piracy by the US Navy,” reads the statement.

Trump said on Friday that the naval blockade of Iranian ports would continue until a deal was agreed by the two countries.

The conflict began with US and Israeli strikes across Iran on 28 February and continued with waves of attacks across the Middle East for five weeks until a two-week truce was declared.

Trump announced the naval blockade after a first round of negotiations earlier this month ended without an agreement. Key issues, including Iran’s nuclear programme and control of the Strait of Hormuz – a key oil transport route – remain in contention.

Earlier on Sunday, Trump said his representatives would arrive in Pakistan, which has been mediating between the two, on Monday. The ceasefire is due to expire on Wednesday.

A White House official told the BBC that, as well as Vance, the delegation would include Trump advisers Steve Witkoff and Jared Kushner, who were both also present at the previous talks.

But Iran’s state news agency IRNA said reports of a second round of talks with the US were “not true”.

It added that the US blockade, along with “excessive” demands and threatening rhetoric from Washington, had “so far hindered the progress of the negotiations”.

Nevertheless, preparations for further discussions have begun in the Pakistani capital, Islamabad.