David Cameron has urged Israel to do "as little as possible to escalate" tensions in the Middle East, ahead of talks with PM Benjamin Netanyahu.
Israel has vowed to retaliate after Iran's unprecedented missile and drone attack at the weekend.
The UK foreign secretary will push Israel to rein in the scale of its response over fears it could lead to a regional wider war.
He called on Israel's government to be "smart as well as tough".
Speaking to reporters shortly after arriving in Jerusalem on Wednesday, Cameron said he was there to "show solidarity after that appalling attack by Iran".
He continued: "It's right to have made our views clear about what should happen next, but it's clear the Israelis are making a decision to act.
"We hope they do so in a way that does as little to escalate this as possible. And in a way that, as I said yesterday, is smart as well as tough.
"But the real need is to refocus back on Hamas, back on the hostages, back on getting the aid in, back on getting a pause in the conflict in Gaza."
Cameron is one of several Western foreign ministers who are expected to visit Israel in the coming days to convey that message in person - he briefly met German Foreign Minister Annalena Baerbock over breakfast on Wednesday.
Cameron and Ms Baerbock later met Israeli President Isaac Herzog and Israeli Foreign Affairs Minister Israel Katz.
The UK foreign secretary also plans to hold talks with Mohammad Mustafa, the prime minister of the Palestinian Authority.
Later, Cameron will travel to a gathering of G7 ministers in Italy, where he will push for coordinated sanctions on Iran.
He has accused Tehran of being "behind so much of the malign activity" in the Middle East and called for other countries to adopt measures designed to restrict Iran's influence.
"They need to be given a clear unequivocal message by the G7," Cameron said. "And I hope that will happen at the meeting."
The US and European Union are considering further sanctions, and Israel is calling on its allies to designate the Islamic Revolutionary Guard Corps (IRGC) - a major military, political and economic force in Iran - as a terrorist organisation.
The Israeli government has repeatedly vowed to retaliate after Iran sent more than 300 drones and missiles towards Israel in an unprecedented direct attack overnight on Saturday.
Almost all the projectiles were intercepted by Israel's air defence systems, with the help of the UK, US, France, and Jordan.
Iran's direct attack on Israel was carried out in response to a strike in Syria on 1 April which killed senior Iranian military figures. Israel has not publicly confirmed it was behind the attack, but is widely believed to have been.
On Tuesday evening, UK Prime Minister Rishi Sunak spoke to Mr Netanyahu and warned that "significant escalation will only deepen instability in the region", adding: "This is a moment for calm heads to prevail."
Cameron will seek to reinforce Mr Sunak's call for restraint during his visit to Israel, and put more pressure on its leaders to do more to allow humanitarian aid into Gaza - but he is walking a delicate diplomatic line.
The foreign secretary will not want to appear to be hectoring an ally which has just been subject to an unprecedented attack on its soil.
That is why Cameron is also talking about the need for Hamas to release hostages and the importance of western powers imposing yet more sanctions on Iran.
His presence in Jerusalem is a show of support and solidarity - but also an attempt to warn Israeli leaders that any significant escalation would be against their interests and the world's.
Source: BBC