A giant screen (above) displays a picture of Holocaust survivors in a tent at the entrance to the former Auschwitz Nazi concentration camp during a ceremony in Oswiecim, Poland, on Tuesday to mark the 70th anniversary of the camp's liberation. Top: Aging survivors gather at the site to honor victims and sound the alarm over a fresh wave of anti-Semitism. AFP / AP

About 300 survivors of the Auschwitz death camp were gathering on Tuesday to mark 70 years since its liberation by Soviet troops.

They were being joined by world leaders for a commemoration held in the shadow of war in Ukraine and a rise in anti-Semitism in Europe.

The gathering in southern Poland marked perhaps the last major anniversary that survivors of the Nazi camp will be able to attend in numbers, given that the youngest are now in their 70s. Some 1,500 attended the 60th anniversary.

About 1.5 million people, mainly European Jews, were gassed, shot, hanged and burned at the camp during World War II before the Red Army entered its gates in winter 1945. It has probably become the most poignant symbol of a Holocaust that claimed 6 million Jewish lives across Europe.

French President Francois Hollande, German President Joachim Gauck and Ukraine President Petro Poroshenko took part in the commemoration along with a dozen other leaders, but Russia, the United States and Israel chose to send lower-ranking representatives.

European Jews warn of a growing undercurrent of anti-Semitism, fueled by anger at Israeli policy in the Middle East and social tensions over issues of immigration, inequality and economic hardship that have contributed to a rise of far-right political movements.

Gauck warned on Tuesday that Germany's Holocaust history should not be forgotten and called for a continued coexistence of different cultures and religions in his country.

On the eve of the anniversary, German Chancellor Angela Merkel said Germans have an everlasting responsibility to fight all forms of anti-Semitism and racism.

"We've got to constantly be on guard to protect our freedom, democracy and the rule of law," Merkel said. "We've got to expose those who promote prejudices and conjure up boogeymen - the old ones as well as the new."

Hollande, telling French Jews that "France is your homeland," described as "unbearable" the rise in anti-Semitic attacks in France, underscored by the Islamist killings at a kosher supermarket in Paris earlier this month.

Auschwitz's victims also included, among others, Roma, homosexuals and political opponents of the Nazis.

David Wisnia, an 88-year-old survivor of the camp, said the Holocaust is almost impossible for a human mind to comprehend.

A choirboy as a child at Warsaw's Great Synagogue, which was blown up by Nazi forces in 1943, Wisnia was due to sing a memorial prayer in Hebrew on Tuesday.