The British public are “revolted” at scenes of desperation in Gaza, Sir Keir Starmer said.
The Prime Minister, appearing alongside Donald Trump at his Turnberry golf course in Scotland, described the situation in the Palestinian territory as an “absolute catastrophe”.
It comes as senior ministers plan to meet this week to discuss the crisis in the Middle East.
Sir Keir is expected to urge the US president to apply pressure on Israel to allow more humanitarian aid into Gaza, where the population is facing starvation.
“It’s a humanitarian crisis, it’s an absolute catastrophe,” the Prime Minister said of the situation in Gaza as he arrived in Ayrshire.
He added: “Nobody wants to see that. I think people in Britain are revolted at seeing what they’re seeing on their screens, so we’ve got to get to that ceasefire.”
Israel announced at the weekend that it would suspend fighting in three areas of Gaza for 10 hours a day and open secure routes for aid delivery, while the UK confirmed it was taking part in plans led by Jordan to airdrop aid into the territory.
Sir Keir is expected to present a UK-led plan to bring peace to the Middle East to Mr Trump and other allies in the coming days, Downing Street indicated.
Work on the plan began alongside France and Germany over the weekend after a call with the two countries’ leaders, Emmanuel Macron and Friedrich Merz.
Writing in the Mirror newspaper on Friday, the Prime Minister likened the plan to the international effort to support Ukraine towards a lasting peace, the coalition of the willing.
The Prime Minister’s official spokesman said the plan would build “on the collaboration to date that paves the way to a long-term solution on security in the region”.
He added: “As I’ve said, the Prime Minister will be presenting that plan to other key allies, including the USA and Arab states, over the coming days, and indeed convening Cabinet this week. You can expect to see more coming out of that.”
There is no indication yet of which day this week the Cabinet meeting – which gathers together the government’s most senior ministers – will take place.
The Prime Minister is meanwhile facing calls from a growing number of MPs to immediately recognise a Palestinian state.
Palestinians have an “inalienable right to statehood”, and it is a “question of when, not if” the UK will agree to recognition, No 10 said.
More than 250 cross-party MPs have now signed a letter calling for ministers to take the step, up from 221 on Friday.
Business Secretary Jonathan Reynolds earlier dismissed the idea that there is a split at the top of government over when to recognise a Palestinian state.
Health Secretary Wes Streeting is among those to have signalled a desire for hastened action calling for recognition “while there’s still a state of Palestine left to recognise”, while Justice Secretary Shabana Mahmood said the government wants to recognise a Palestinian state “in contribution to a peace process”.
Speaking to Good Morning Britain, Mr Reynolds said: “There’s no split. The whole of the Labour Party, every Labour MP, was elected on a manifesto of recognition of a Palestinian state, and we all want it to happen.
“It is a case of when, not if.”
