Two-in-three Americans between the ages of 18 and 34 years old cannot say what Auschwitz was, according to a study released Thursday, known internationally as Holocaust Remembrance Day.

Sixty-six percent of millennials and 41 percent of all U.S. adults could not explain the significance of Auschwitz, which was a Poland-based concentration and extermination camp where the Nazis held 1.3 million people and killed 1.1 million during World War II.

Among Millennials, 41 percent believe fewer than 2 million Jewish people were killed during the Holocaust - one-third of the actual number, according to the Conference on Jewish Material Claims Against Germany's Holocaust Knowledge and Awareness Study.

“On the occasion of Yom HaShoah, it is vital to open a dialogue on the state of Holocaust awareness so that the lessons learned inform the next generation. We are alarmed that today’s generation lacks some of the basic knowledge about these atrocities," Claims Conference President Julius Berman said in a statement.

More than half of all Americans, 58 percent, worry a mass genocide could happen again.

More than 9-in-10 people say students should learn about the Holocaust at school, though 80 percent say they have never visited a Holocaust museum.

The Feb. 23-28 survey was conducted by Schoen Consulting among 1,350 U.S. adults by phone and online. The poll as a whole had a 3 percentage point margin of error. Millennials made up 31 percent of all respondents and had a 5 percentage point margin of error.