Sir Keir Starmer has arrived in Saudi Arabia as he visits Gulf allies after the US and Iran agreed on a two-week ceasefire.

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".

Sir Keir said: "I welcome the ceasefire agreement reached overnight, which will bring a moment of relief to the region and the world."

He added: "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."

Sir Keir is also expected to meet UK military personnel in the region as part of his Gulf trip, which was planned before the ceasefire announcement.

For the Conservatives, shadow housing secretary Sir James Cleverly told BBC Breakfast the ceasefire is an "opportunity for Iran to make some serious choices" about how it behaves at home and abroad.

Former foreign secretary Sir James said the war was initiated to ensure Iran "never acquires a nuclear weapon" and that remains an "absolute priority", adding: "So we'll welcome this two-week ceasefire, but it's time that mustn't be wasted."

Liberal Democrat leader Sir Ed Davey welcomed the ceasefire but questioned whether the UK could trust Trump, labelling him a "totally unreliable ally".

Sir Ed said the Strait of Hormuz needed to be opened, otherwise people would "pay a heavy price in inflation and lower growth", adding: "So whatever it takes, but I do think we've got to stand up to America.

"America has caused this problem so we've got to work with allies who we can trust."

Last week the UK hosted a virtual summit in which representatives from more than 40 countries began work to assemble a coalition capable of ensuring security in the Strait after the fighting has stopped.

This was followed by a military planning conference on Tuesday.

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 coordinated 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 transit.

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.