The UN's top official called the war in Gaza a "mark of collective political failure" on Saturday during a Holocaust memorial service in New York. Secretary-General Ban Ki-moon, who had regained his voice after losing it during his whirlwind diplomatic tour of the Middle East last week, blamed Palestinians, Israelis and the international community equally for the outbreak of violence. "I said to all I met, on both sides, 'This must stop,'" Ban told congregants at the Park East Synagogue in Manhattan. He said he was "more determined than ever" to seek a durable two-state peace accord. Ban appeared as the guest speaker at the Modern Orthodox congregation's annual Holocaust remembrance commemoration. Diplomats from Israel, Germany, Austria and other nations joined him in the ornate sanctuary. Rabbi Arthur Schneier asked the assembled dignitaries in his opening remarks to do their best to help "bring about shalom." But he also asked the diplomatic corps to take seriously threats made against Israel or any other nation. "Take the word of any demagogue, of any tyrant, of any dictator at face value - they mean what they say," warned Schneier, who survived Kristallnacht. He invited his fellow survivors - an ever-shrinking and graying group - to stand, and also called on the Rwandan ambassador to rise and bear witness to his country's genocide 15 years ago. Ban responded in his remarks that he had twice rebuked Iranian President Mahmoud Ahmadinejad for saying that Israel should be "wiped off the map." He did not explicitly name Hamas, but acknowledged that a million Israelis have been living in "a daily state of terror" from rocket fire, including a child and his parents he met in Sderot, but condemned the "appalling devastation" in Gaza. Ban also asserted the role of the UN in reaching a solution. He recalled fleeing war in his native South Korea as a six-year-old and defended the "transformative power" of the UN in war-torn regions. Ban's appearance, his first formal speech at a synagogue, came as Jewish groups in the US decried the planned participation of Miguel d'Escoto Brockmann, a Nicaraguan diplomat who currently holds the one-year presidency of the UN General Assembly, in a UN Holocaust remembrance ceremony scheduled for Tuesday. D'Escoto, who in November compared Israel to apartheid South Africa at a UN session devoted to the plight of the Palestinian people, attracted criticism from Jewish groups and Israeli diplomats after publicly hugging Ahmadinejad at the UN in September. The Conference of Presidents of Major American Jewish Organizations and B'nai B'rith International both released statements Friday condemning d'Escoto's appearance. "As a constant voice of division and anti-Israel rhetoric, d'Escoto has practiced a consistent policy of bias that impairs his ability to play a positive role in events dedicated to remembering and honoring the victims of the Holocaust," B'nai B'rith said in its statement. A spokesman for d'Escoto declined to comment and said the diplomat would attend the ceremony as planned. Israeli Ambassador to the UN Gabriela Shalev is also slated to speak, as is Tel Aviv Chief Rabbi Yisrael Meir Lau, chairman of the Yad Vashem Council and a Holocaust survivor himself.