ReutersKeir Starmer welcomed the ceasefire agreement between Iran and the US as he travelled to meet with leaders of countries in the Gulf on Wednesday.
The prime minister is expected to "discuss diplomatic efforts to support and uphold the ceasefire", according to No 10. He will return to the UK on Friday.
The ceasefire comes after Donald Trump threatened "a whole civilisation will die" if Iran did not agree to end the war and unblock the Strait of Hormuz - comments that led Downing Street to call again for "de-escalation".
"I welcome the ceasefire agreement reached overnight, which will bring a moment of relief to the region and the world", Starmer told reporters on Wednesday.
"Together with our partners we must do all we can to support and sustain this ceasefire, turn it into a lasting agreement and reopen the Strait of Hormuz", he added.
Iran and the US agreed to the conditional ceasefire on Tuesday, just over an hour before the expiry of the deadline Trump had set for Iran to make a deal.
In a post on Truth Social, Trump said the ceasefire was "subject to the Islamic Republic of Iran agreeing to the COMPLETE, IMMEDIATE, and SAFE OPENING of the Strait of Hormuz".
Meanwhile, the Iranian Foreign Minister Abbas Araghchi announced Iran would agree to a ceasefire "if attacks against Iran are halted".
"For a period of two weeks, safe passage through the Strait of Hormuz will be possible", he added.
The war began in February, when the US and Israel launched co-ordinated attacks on Iran over concerns Tehran was accelerating efforts towards building a nuclear weapon.
In response, Iran has launched strikes on its neighbours across the Gulf and the wider Middle East.
It also placed a stranglehold on the Strait of Hormuz, a waterway that serves as a critical shipping route through which a fifth of the world's energy shipments usually transits.
The conflict caused the price of crude oil to spike, with sharp increases in petrol and diesel costs, leading to concerns about the cost of living in countries across the world.
