Donald Trump has said the US will begin blockading the strait of Hormuz in an attempt to take control of the strategic waterway from Iran in the aftermath of failed peace negotiations between the countries in Pakistan.

The US president also threatened to bomb Iran’s water treatment facilities as well as its power plants and bridges, repeating an earlier threat, if Tehran did not agree to abandon its nuclear weapons programme – the key sticking point between the two sides.

Trump’s surprise announcement of a blockade came after 21 hours of face-to-face peace negotiations between the US and Iran in Islamabad collapsed on Sunday morning.

JD Vance, the vice-president and head of the US team, said Iran had refused to give up the possibility of developing nuclear weapons, while the Iranian delegates said Washington needed to do more to win their trust.

Risking another increase in oil prices, Trump said he had instructed the US navy to begin “blockading any and all ships trying to enter, or leave, the strait of Hormuz” – and accused Iran of extortion with its own scheme of charging tolls to tankers.

Iran’s Revolutionary Guards responded by declaring that if any warships approached the strait to enforce a blockade – usually considered an act of war – it would be considered a breach of the current ceasefire and would be strongly dealt with. They insisted the strait remained under Iranian control.

Two US destroyers nevertheless crossed and recrossed the strait without incident on Saturday, although Iranian media said they had been threatened as they left. It was the start of a broader mine clearance mission, the US military said.

The president added that US warships would “seek and interdict every vessel” that had paid Iran since the start of the conflict and begin de-mining the central section of the strait, previously declared a “hazardous area” by Tehran, although it is unclear how many mines have actually been laid.

About 100 tankers have transited the strait since the US and Israel started bombing Iran, paying up to $2m each time for passage. Many were bound for China and India, carrying Iranian oil products, and chasing them down could complicate relations between the US and the importing.

The US and Iranian delegations left Pakistan soon after the talks ended. Vance said he had spoken with Donald Trump at least half a dozen times during the talks, held during a 14-day ceasefire announced by the US, Israel and Iran overnight on 7 and 8 April.

“We need to see an affirmative commitment that [Iran] will not seek a nuclear weapon, and they will not seek the tools that would enable them to quickly achieve a nuclear weapon,” Vance said. “That is the core goal of the president of the United States, and that’s what we’ve tried to achieve through these negotiations.”

Mohammad Bagher Ghalibaf, the speaker of the Iranian parliament, who had led Tehran’s negotiators, said that, although he and his colleagues had offered “constructive initiatives”, the US had been “unable to gain the trust of the Iranian delegation in this round of negotiations”.

Iran’s semi-official Tasnim news agency said “excessive” US demands had hindered reaching an agreement, but the foreign ministry said more time was needed. “Naturally, from the beginning we should not have expected to reach an agreement in a single session,” the ministry’s spokesperson, Esmail Baghaei said, according to the state broadcaster IRIB.

Pakistani mediators called on the US and Iran to refrain from renewing hostilities and said they would try to arrange a fresh round of talks. “It is imperative that the parties continue to uphold their commitment to the ceasefire,” said Pakistan’s foreign minister, Ishaq Dar.

Vance was accompanied by US special envoy Steve Witkoff and Trump’s son-in-law Jared Kushner. They met Ghalibaf and the foreign minister, Abbas Araghchi, for several negotiating sessions at the Serena hotel in Islamabad, with Pakistan’s powerful army chief, Asim Munir, also present.

Iran’s delegation arrived on Friday dressed in black in mourning for the late supreme leader Ayatollah Ali Khamenei and others killed in the war. They carried shoes and bags of children killed during the bombing of a school next to a military compound, the Iranian government said.

A Pakistani source said the discussions, the highest level direct contact between the US and Iran since 1979, were unpredictable in tone. “There were mood swings from the two sides, and the temperature went up and down during the meeting,” a Pakistani source said after the first round.

In a subsequent Fox News interview, Trump threatened to restart the bombing of Iran if a deal could not be agreed, and threatened to target the country’s water supply as well as its bridges and power generation.

Trump said: “The only thing left, really, is their water, which would be very devastating to hit. I would hate to do it, but it’s their water, their desalinisation plans, their electric generating plants, which are very easy to hit.”

The president was also asked if gas and oil prices might be lower by the US midterms in November, an indication that attacking Iran was not an economic mistake. Prices “could be the same or maybe a little bit higher,” a non-committal Trump replied.

At least 11 were also reported killed in southern Lebanon by the country’s state news service, after at least 30 Israeli strikes in the region. Pope Leo XIV called for a ceasefire after his Sunday prayers, and said he felt “closer than ever” to the country’s people.

The war, which began with US and Israeli strikes on Iran six weeks ago, has killed at least 3,000 people in Iran, 2,020 in Lebanon, 23 in Israel and more than a dozen in Gulf Arab states. It has caused lasting damage to infrastructure in half a dozen Middle Eastern countries.