The Archbishop of Canterbury joined the Chief Rabbi to mark Holocaust Memorial Day with a ceremony in Liverpool.
More than 1,600 people, including Holocaust survivors, attended the service at the Philharmonic Hall.
The service marked the 1945 liberation of the Auschwitz-Birkenau concentration camp but victims of other atrocities were also remembered.
Leaders of several faiths listened to personal testimony and called for an end to genocide throughout the world.
Dr Rowan Williams and Sir Jonathan Sacks signed a Pledge Against Genocide in the form of a large mural.
'Mass graves'
The ceremony included personal testimony from survivors and relatives, poetry, music and speeches.
Among the speakers was the Reverend Leslie Hardman, who helped to liberate the Bergen-Belsen concentration camp as a British solider.
Kay Fyne, from Liverpool, spoke of her memories of being taken to the camp as a child.
The Royal Liverpool Philharmonic Orchestra and a 100-strong community choir performed for the event which explored the Jewish experience of the Holocaust with the theme, Imagine: Remember, Reflect, React.
Liverpool-born actor Jason Isaacs, who plays Lucius Malfoy in the Harry Potter films, recited testimonies from survivors.
'Never forget'
The Muslim Council of Britain ended its boycott of the event. It had wanted more recognition of atrocities in other parts of the world, such as Bosnia and Chechnya.
Communities and Local Government Secretary Hazel Blears introduced a video-message from Prime Minister Gordon Brown in which he urged people to "never forget" the Holocaust.
The service ended with the performers trooped out of the hall singing We're All in the World Together, holding candles as they filed out.
Christine Shaw, of the Holocaust Memorial Day Trust, said the event aimed to "reflect on the lessons society can learn from the Holocaust and other genocides in an effort to tackle the intolerance and prejudice that still exists in the UK today".
Karen Pollock, of the Holocaust Educational Trust, told BBC Radio Five Live it was important to make what had happened in the past relevant to today.
"The fact is that racism still exists, that genocide is taking place in Darfur, and genocide has happened since the Holocaust, for instance Cambodia [and] Rwanda.
"This is an opportunity for people to come together and say 'never again' and mean it and act upon it."
Former BBC war correspondent and independent MP Martin Bell was also present.
Mr Bell said: "The mass graves and memorials at Srebrenica, or the piles of skulls heaped in Cambodian Stupas, are just a few reminders of the millions of people killed in politically orchestrated acts of ethnic cleansing since the Holocaust."
Interpretation
Events are being held across the UK and more than 2,000 schools are taking part during the course of the week.
They include:
An Anne Frank play performed by children at King's School in Rochester, Kent.
Scouts will plant trees near Lewes, Sussex, and a service will be held at the North West Surrey Synagogue, in Weybridge.
Schools in Lewisham, London, will present their interpretation of the theme through dance, drama, songs and readings.
Commemorative multi-faith services in Barnet, Haringey, Lewisham, Tower Hamlets and Romford.
An exhibition of paintings and stained glass by Moshe Gallili, a Holocaust survivor, in Enfield.
Holocaust survivor, Steven Frank, will tell his story during an evening at Reading Council Chamber on Thursday, which will be followed by a panel debate on extremism.