Holocaust survivors gathered in Poland to mark the 70th anniversary of the liberation of Auschwitz-Birkenau death camp.

NPR noted that on Tuesday, Holocaust Remembrance Day, survivors along with several world leaders, marked the anniversary.

“Among the leaders who will be attending the Auschwitz ceremony are the presidents of Germany and Austria, the nations that gave rise to the Nazis and have since tried atoning for their sins,” said the station’s Soraya Sarhaddi Nelson.

Perhaps most notable though, she added, is that Russian President Vladimir Putin was not in attendance.

The concentration camp was liberated by the Russians in 1945.

U.S. President Barack Obama released a statement addressing the survivors.

“The American people pay tribute to the six million Jews and millions of others murdered by the Nazi regime,” the statement read. “We also honor those who survived the Shoah, while recognizing the scars and burdens that many have carried ever since.”

Of the more than 1 million people killed in the extermination camp, 90 percent of them were Jewish. Others murdered included Soviet prisoners of war, Jehovah's Witnesses and homosexuals.