Sir Keir Starmer has urged the US and Iran “to find a way through” after the failure of peace talks, as Donald Trump said the US would blockade the Strait of Hormuz.
The Prime Minister also called for the fragile ceasefire to continue and warned against any further escalation.
But the US president cast fresh uncertainty over any hope of a fast resolution to the conflict as he lambasted Iran for failing to release its grip on the vital oil and gas shipping lane and commit to giving up its nuclear ambitions.
In a lengthy post on his Truth Social platform after the peace talks ended without a deal, Mr Trump said the US would “immediately” start “BLOCKADING any and all Ships trying to enter, or leave, the Strait of Hormuz”.
He added that the US navy would also “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 added, without elaborating: “Other Countries will be involved with this Blockade.”
He said talks in Pakistan involving US Vice-President JD Vance “went well, most points were agreed to, but the only point that really mattered, NUCLEAR, was not”.
Sir Keir discussed Washington and Tehran’s negotiations with the Sultan of Oman after the two sides’ 21-hour session ended without an agreement in the early hours of Sunday.
In a readout of Sir Keir’s call with His Majesty Sultan Haitham bin Tarik al Said, a Downing Street spokeswoman said: “They discussed the peace talks held in Pakistan over the weekend and urged both sides to find a way through.
“It was vital there was a continuation of the ceasefire, and that all parties avoided any further escalation, the leaders agreed.”
They also discussed efforts to reopen the Strait of Hormuz, which has been throttled by Iran, sending energy prices soaring.
Britain will host further talks on reopening the maritime pinch-point with a coalition of countries next week.
According to the call readout: “His majesty updated on the situation in the Strait of Hormuz, and the Prime Minister thanked him for Oman’s efforts to rescue sailors from vessels in distress in the region.
“Reflecting on international efforts to co-ordinate safe passage for shipping in the region, the Prime Minister said that following meetings convened by the Foreign Secretary and British military planners, partners continued to work towards restoring freedom of navigation for the long term.”
The meeting next week is expected to look for ways to support a sustainable end to the conflict and focus on increasing international diplomatic pressure on Iran to reopen the strait, according to an official with knowledge of the planning.
This includes exploring co-ordinated economic and political measures, such as sanctions, and working with the International Maritime Organisation to secure the release of thousands of ships and sailors trapped in the strait.
It would be the third meeting hosted by Britain regarding the issue this month, following a virtual meeting of more than 40 nations convened by the Foreign Secretary and a gathering of allied military officers.
The Prime Minister visited allies in the Gulf this week for talks on how to support what he described as a “fragile” ceasefire.
Gulf nations have borne the brunt of Tehran’s retaliation for the US-Israeli campaign against it, with thousands of Iranian missiles and drones targeting US military sites and energy infrastructure there.
Mr Trump agreed a two-week ceasefire earlier this week, with the reopening of the Strait of Hormuz a key condition, shortly after warning Iran that “a whole civilisation will die” if it did not meet his demands.
Health Secretary Wes Streeting criticised Mr Trump’s “incendiary, provocative, outrageous” language, and said ministers had learned to draw a distinction between what the American leader “says and what he does”.
Disagreements over the Iran war, Greenland and the Chagos Islands, as well as the US president’s repeated jibes against the UK, had “undoubtedly strained” UK-US relations, the senior minister added.
