The Strait of Hormuz must be reopened with “unconditional and unrestricted” access for shipping, Sir Keir Starmer said as a US-Iran deal appeared to be drawing closer.
US President Donald Trump has said a deal with Iran, which would including opening the strait, a vital oil and gas shipping route, has been “largely negotiated”.
Mr Trump said “final aspects of the deal” are currently being discussed.
The Prime Minister said the UK would work with allies to “seize this moment” to help achieve a long-term solution in the Middle East.
Sir Keir said: “I welcome the progress towards an agreement between the US and Iran.
“We need to see an agreement that brings the conflict to an end and reopens the Strait of Hormuz, with unconditional and unrestricted freedom of navigation.
“It’s vital that Iran must never be allowed to develop a nuclear weapon.
“My Government will continue to do everything we can to protect British people from the impact of this conflict.
“We will work with our international partners to seize this moment and achieve a long-term diplomatic settlement.”