Some 70 former inmates attended a service at the Bergen-Belsen Nazi death camp on Sunday to mark 70 years since it was liberated.
German President Joachim Gauck thanked the British military for opening the gates to the camp in Lower Saxony at the end of World War II.
"The British soldiers were ambassadors of a democratic culture that was not intent on revenge on the enemy, but rather that justice and human dignity should be afforded new validity even in Germany," Gauck said at the memorial service at the site of the camp on Sunday.
It was a "deeply felt need" to thank the liberators from the heart, Gauck said.
Lower Saxony Premier Stephan Weil also appealed that the crimes of the Nazis never be forgotten. "Murder never falls beyond the reach of justice, mass murder and genocide should most certainly never ever do so," Weil said.
He said Germany must deal decisively with any sign of racism, xenophobia or right-wing extremism.
"If refugees fear arson attacks, if Jews in Germany feel insecure once more, if people feel excluded because of their faith, then we must not accept it and just go back to normal," Weil said.
When the British Army liberated the camp, which lies near the town of Celle on the Lueneburg Heath, they found some 10,000 corpses within its grounds.
Nothing remains of the barracks which housed the inmates, just open land under which mass graves are located.
Some 200,000 people were deported to Bergen-Belsen during the war, with more than 70,000 believed to have been killed there, among them the 15-year-old diarist Anne Frank.
Another service was scheduled to take place on Sunday at Flossenbuerg in Bavaria to mark the liberation of a concentration camp there by the U.S. Army.
Forty survivors were expected to take part in that ceremony.
At least 30,000 people were imprisoned at Flossenbuerg by the Nazis.
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