- The UK prime minister agreed to work with Saudi Crown Prince Mohammed bin Salman to avoid further escalation and deliver aid to Gaza.
- Mr Sunak flew to Riyadh as part of a two-day trip to capitals in the region.
Rishi Sunak has urged Saudi Arabia to help support stability in the Middle East, after backing Israel in its war with Hamas on a visit to the country.
The UK prime minister agreed to work with Saudi Crown Prince Mohammed bin Salman to avoid further escalation and deliver aid to Gaza.
Mr Sunak flew to Riyadh as part of a two-day trip to capitals in the region.
Earlier, Mr Sunak promised to stand with Israel in a meeting with Prime Minister Benjamin Netanyahu.
The diplomatic flurry comes as Israel prepares for a ground invasion into Gaza after the deadly Hamas attack on 7 October.
Speaking at a joint press conference with Mr Netanyahu, Mr Sunak said he was "proud" to support Israel in its "long war" against Hamas, which he branded "pure evil".
"We will stand with you in solidarity, we will stand with your people. And we also want you to win," Mr Sunak told reporters.
In a statement following the meeting with the Saudi crown prince, Downing Street said the pair agreed the "loss of innocent lives in Israel and Gaza over the last two weeks has been horrific" and "underscored the need to avoid any further escalation in the region".
Mr Sunak "encouraged the crown prince to use Saudi's leadership in the region to support stability, both now and in the long-term", No 10 said.
Israeli warplanes and artillery have been bombarding Gaza since more than 1,400 people were killed in the attack by Hamas earlier this month.
Gaza remains under siege, with Israel blocking cross-border supplies of water, electricity, and fuel.
Downing Street said Mr Sunak had met his Israeli counterpart for two hours of talks, mostly without officials present.
Appearing afterwards, Mr Netanyahu said Israel would need "continued support" from allies, warning there would be "ups and downs" and "difficulties" as it fought Hamas.
Speaking alongside him, Mr Sunak told reporters the UK "absolutely" supported Israel's "right to defend itself, in line with international law".
"I know that you are taking every precaution to avoid harming civilians, in direct contrast to the terrorists of Hamas," he added.
'Darkest hour'
Borrowing a phrase from Britain's leader during World War Two, Sir Winston Churchill, Mr Netanyahu said the Hamas attack represented "the world's darkest hour".
Mr Sunak echoed the language, adding: "I'm proud to stand here with you in Israel's darkest hour as your friend".
His visit comes directly after US President Biden's, as world leaders step up efforts to prevent the conflict spilling into the wider region.
Mr Biden said Israel had been "badly victimised" - and had a right to strike back against Hamas.
But he cautioned Israelis against being "consumed" by anger, urging them not to repeat the "mistakes" made by an "enraged" United States after the 9/11 attacks in 2001.