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.

Guests at the hotel where the talks took place between the US and Iranian delegations last weekend were told they needed to leave, the BBC's Pakistan correspondent reported.

Pakistan's Prime Minister Shehbaz Sharif spoke to Iran's President Masoud Pezeshkian on Sunday evening, according to a statement released by his office. It did not make any mention of further talks between Iran and the US.

The Strait of Hormuz remained closed on Sunday, a day after the Islamic Revolution Guard Corps (IRGC) said it was ending a temporary reopening over the US blockade, which it said violated the terms of their ceasefire agreement. Iran said it would stay closed until the US ended its naval blockade.

About 20% of the world's oil and liquefied natural gas (LNG) is usually transported through the strait. The number of ships making the journey has dramatically decreased during the recent conflict, which has caused global energy prices to soar.

Trump has said Iran cannot "blackmail" the US with threats regarding the waterway.

He threatened to knock out every bridge and power plant in Iran if Tehran did not agree to a peace deal.

"If they don't take the DEAL, it will be my Honour to do what has to be done," Trump wrote in another Truth Social post on Sunday.

The US president also accused Iran of violating the ceasefire by attacking ships in the Strait of Hormuz on Saturday. He said these included a French ship and a freighter from the UK.

French shipping company CMA CGM confirmed that one of its vessels was fired at, telling news agency AFP that it "was the target of warning shots". There were no reports of attacks on UK-linked ships on Saturday, according to both the UK's defence and transport ministries.

There were two reports of ships - a tanker and cargo ship - being attacked in the strait on Saturday, according to the UK Maritime Trade Operations. The maritime security agency gave no further information on which nations the vessels were linked to.

Meanwhile, India said two Indian-flagged ships were involved in a shooting incident in the area.

Traffic in the Strait of Hormuz remained at a standstill on Sunday, according to data from tracking site MarineTraffic.

The IRGC-affiliated Tasnim news agency said two tankers "sailing under the flags of Botswana and Angola" wanted to travel through Hormuz but were "forced to change course and retreat due to the timely action of the armed forces of Iran".