Tehran must reopen the Strait of Hormuz for shipping as part of the deal.
Sir Keir Starmer has arrived in Saudi Arabia as he visits Gulf allies to push for a long-term resolution to the Iran conflict.
It comes after Iran and the US agreed to a two-week ceasefire on the condition that Iran reopens the Strait of Hormuz for shipping.
The Prime Minister is set to hold talks with Gulf leaders on how best to support the pause in fighting and ensure passage is permanently restored through the key oil and gas shipping route.
Sir Keir is also expected to thank armed forces from the UK and allied countries who are posted in the region.
