During a speech at the US Holocaust Museum, to mark Yom HaShoah, or the Holocaust Remembrance Day, President Obama referred directly to the gay victims of Nazi persecution, pleading that the task of today’s generation is for the atrocities of the genocide should occur “never again.”

The Holocaust, or Shoah, is the term used to denote the systematic killing of an estimated six million people, as part of the racial and social ideologies of the Nazi regime under Adolf Hitler. The most numerous of these victims were Jewish people from every corner of Europe that fell under German occupation in the lead up to and during the Second World War.

Addressing an audience of around 250 people, Mr Obama said: “We must tell our children about a crime unique in human history… The one and only Holocaust — six million innocent people — men, women, children, babies — sent to their deaths just for being different, just for being Jewish. We tell them, our children, about the millions of Poles and Catholics and Roma and gay people and so many others who also must never be forgotten.”

He added: “We must tell our children… But more than that, we must teach them. Because remembrance without resolve is a hollow gesture. Awareness without action changes nothing. In this sense, ‘never again’ is a challenge to us all — to pause and to look within.”

He also used the speech to announce an executive order he signed, authorising sanctions on Syria and Iran.

The mention of homosexuals is thought to be significant, as he failed to do so in his speech two years ago, which commemorated the 65th anniversary of the liberation of the Auschwitz concentration camp.

Previously, both the United Nations, and the former Prime Minister of Britain, Gordon Brown, paid tribute to gay victims when remembering the Holocaust.

An estimated 100,000 homosexual men were arrested by the Nazis, an unknown number of whom perished in the concentration camps, who often met the worst of the fates during their interment. Forced to wear a pink triangle as a badge marking the reason for their imprisonment, they met cruel treatment not just at the hands of the Nazis, but, according to historians, even from fellow prisoners.

Yet, far from being acknowledged as victims of persecution, many of them were re-arrested after the end of the Second World War, and were not released until much later. As such, homosexuals became one of the “forgotten victims,” whose persecution it took Germany, and Europe at large, several decades to acknowledge. Admitting to this silence, the memorials for gay victims at Cologne and at Dachau, with the latter bearing the figure of the pink triangle, contain the expression: ‘Totgeschlagen. Totgeschweigen,’ which, translated, can be rendered as: ‘Struck Dead, Hushed-up.’

The pink triangle was subsequently appropriated by LGBT rights activists for the gay liberation movement.