In a message seen as aiming to repair a rift with the Jewish community, President Donald Trump used the occasion of Yom Hashoah to pledge “never again” and to make a pointed reference to Iran.

Mr Trump sent a four-minute long video message to the World Jewish Congress plenary assembly in New York, calling the Holocaust “the darkest chapter of human history”.

He said: “The mind cannot fathom the pain, the horror and the loss. Six million Jews, two-thirds of the Jews in Europe, murdered by the Nazi genocide. They were murdered by an evil that words cannot describe, and that the human heart cannot bear.

“On Yom HaShoah, we look back at the darkest chapter of human history. We mourn, we remember, we pray, and we pledge: ‘Never again.’”

Mr Trump, whose administration was widely criticised in January for failing to mention Jews in a statement about Holocaust Remembrance Day, and whose White House Press Secretary, Sean Spicer, was caught up in a row about Hitler earlier this month, added: “We must stamp out prejudice and antisemitism everywhere it is found. We must defeat terrorism, and we must not ignore the threats of a regime that talks openly of Israel’s destruction.”

He told the WJC delegates: “On this Holocaust Remembrance Day, we tell the stories of the fathers, mothers and children, whose lives were extinguished and whose love was torn from this earth. We also tell the stories of courage in the face of death, humanity in the face of barbarity, and the unbreakable spirit of the Jewish people.”

And underlining his support for Israel, Mr Trump declared: “Today, only decades removed from the Holocaust, we see a great nation risen from the desert and we see a proud Star of David waving above the State of Israel. That star is a symbol of Jewish perseverance. It’s a monument to unyielding strength. We recall the famous words attributed to Theodor Herzl: If you will, it is no dream. If you will it, it is no dream.”

To the consternation of some, but the approval of other Jewish community leaders, the president was due to deliver the keynote address at the US Holocaust Memorial Museum Days of Remembrance ceremony tomorrow.

The week-long Days of Remembrance was first held in 1979 and then later established by Congress as America’s commemoration of the Holocaust.

Since the Museum opened in 1993 every president has participated in its ceremonies, and Presidents Carter and Reagan also participated in previous years.

During the ceremony, six candles are lit by a Holocaust survivor, accompanied by a member of Congress. The annual observance also recognises the American troops who liberated Nazi concentration camps by opening with a procession of flags from each of the US army liberating divisions.