“In Israel's darkest hour as your friend. We will stand with you in solidarity. We will stand with your people and we also want you to win."
Meanwhile in a meeting with Herzog, Sunak said he had "not just a right" but a "duty" to restore security to the country.
After landing at Ben Gurion airport earlier on Thursday, Sunak told reporters on the ground: "Above all, I'm here to express my solidarity with the Israeli people. You have suffered an unspeakable, horrific act of terrorism and I want you to know that the United Kingdom and I stand with you."
As part of the two-day trip, he will also urge other Middle East leaders to "avoid further dangerous escalation", saying that "too many lives have been lost".
Rishi Sunak meets Isaac Herzog in Jerusalem (GPO)
The two-day trip comes after a deadly rocket blast on the Al-Ahli Arab Hospital in Gaza on Tuesday.
The IDF said the blast was caused by a misfired rocket from the Palestinian Islamic Jihad group and released imagery and communications intercepts aimed at supporting their case.
Meanwhile, Hamas claimed an Israeli air strike led to the blast, with Gaza health officials saying it killed at least 500 people.
In a statement ahead of the trip, Sunak said: “Every civilian death is a tragedy. And too many lives have been lost following Hamas’ horrific act of terror.
“The attack on Al Ahli Hospital should be a watershed moment for leaders in the region and across the world to come together to avoid further dangerous escalation of conflict. I will ensure the UK is at the forefront of this effort.”
Earlier on Wednesday, the Prime Minister called for a "calm and cool" response to the blast at the Al-Ahli Arab Hospital.
Refusing to state who was responsible for the blast, he told MPs in the Commons not to "rush to judgment”.
Sunak’s visit comes a day after U.S. President Joe Biden paid a solidarity visit to the Jewish state.
Biden appeared to confirm IDF intelligence reports by telling Netanyahu it "appears as though it was done by the other team, not you".
Reacting to Biden’s comments, Foreign Secretary James Cleverly said: "We take note of what President Biden has said, but we will come to our own judgment, we will work on that quickly, and we will ensure that our assessment is put in the public domain as soon as we are confident of the details."
More than 1,400 people have been killed so far in Israel since the attack earlier this month by Hamas terrorists from the Gaza Strip.
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