Gordon Brown today recalled the Holocaust in a blunt warning to Iran to end its "totally abhorrent" threat to destroy Israel and abandon plans to develop nuclear weapons.
In the first speech by a British prime minister to the Israeli parliament, the Knesset, Brown declared Britain would stand by the country when its "very right to exist" was under threat.
Brown's remarks will be seen as a signal that Britain could be prepared to support a military strike against Iran if all other diplomatic routes fail, including a tightening of sanctions.
In a speech marking the 60th anniversary of the founding of the state of Israel, the prime minister told Israeli MPs: "Britain is your true friend. A friend in difficult times as well as in good times, a friend who will stand beside you whenever your peace, your stability and your existence are under threat."
Brown singled out Mahmoud Ahmadinejad, the Iranian president, who has said Israel should be wiped from the map.
"To those who question Israel's right to exist, and threaten the lives of its citizens through terror, we say: the people of Israel have a right to live here, to live freely and to live in security," Brown said. "And to those who believe that threatening statements fall upon indifferent ears, we say in one voice that it is totally abhorrent for the president of Iran to call for Israel to be wiped from the map of the world."
Brown stopped short of endorsing the comparisons made by Israeli politicians between Ahmadinejad and Adolf Hitler. The prime minister's speech, his toughest to date on Iran, follows an inconclusive meeting with Iran's negotiators on Saturday in Geneva.
Javier Solana, the EU foreign policy chief, has given Iran two weeks to sign up to a package of economic and political support in return for halting the enrichment of uranium.
Brown made clear today the EU will intensify sanctions if Iran does not comply. "Iran now has a clear choice to make: suspend its nuclear programme and accept our offer of negotiations or face growing isolation and the collective response not of one nation but of many nations," he said, to applause from the Knesset members.
Brown's speech marked the end of a two-day visit to Israel and the West Bank, following a one-day visit to Iraq that was carefully balanced to appeal to both sides in the conflict.
In a visit to Bethlehem, which he reached by passing through Israel's controversial separation barrier, Brown announced an extra $60m (£30m) emergency funding to the Palestinian Authority. This is on top of $500m pledged by Britain over three years until 2011.
Speaking at a press conference with the Palestinian president, Mahmoud Abbas, Brown said: "While security is key, Palestinians also need to see real change in their daily lives and that means jobs, housing and basic services."
Brown chose his language with care as he said Palestinians needed to do more to ensure Israel could live in peace. But he indicated the Israeli security barrier was depriving Palestinians of human rights and called on Israel to stop building settlements in the occupied West Bank, which breaks international law. Brown urged Israel to help ease obstacles to economic development among Palestinians.
Brown said: "As a child, I learned about Bethlehem from the Bible as a symbol of peace and a symbol of hope. But today the wall here is graphic evidence of the urgent need for justice for the Palestinian people, the end to the occupation and the need for a viable Palestinian state. There are undoubted problems, the freezing of settlements, stopping of the violence."
The prime minister balanced his visit to the West Bank by symbolically starting the day with a visit to Yad Vashem, Israel's official Holocaust memorial museum. He spent an hour with his wife, Sarah, touring the museum, which chronicles the Nazi extermination programme.
Brown put on a skull cap to rekindle the eternal flame in the Hall of Remembrance and to lay a wreath over the ashes of victims of the six Nazi extermination camps.
He wrote in the visitors' book: "Nothing prepares one for the story that is told here - of the atrocities that should never have happened and the truth that everyone who loves humanity should know."
Israeli MPs heard a personal account from Brown of how he has been a passionate supporter of their country from when he was growing up in the 1950s. Brown told the Knesset he was inspired by his father, John. He used to visit Israel every year in the 1950s and 1960s as a chairman of the Church of Scotland's church and Israel committee and show slides of the building of the new state to his family.
Brown said: "I will never forget those early images of your home and the stories my father would tell. There was never a time that I did not hear about the struggles, sacrifices, tribulation and triumphs as the Israeli people built their new state. I am proud to say that for the whole of my life I have counted myself a friend of Israel."