More than a fifth of millennials in the United States have not heard of or are unsure if they have heard of the Holocaust, a study has found.

Commissioned by the Conference on Jewish Material Claims Against Germany (also known as the Claims Conference), the survey found that many Americans were unaware of basic facts about the Holocaust.

The results were released on Thursday, to coincide with Yom Hashoah, or Holocaust Remembrance Day. The study included 1,350 interviews with Americans aged 18 and over.

While six million Jews are estimated to have been killed in the Holocaust, 31 percent of all respondents and 41 percent of millennials, aged 18 to 34, believe that number is two million or less, according to the survey.

Forty-five percent of all respondents could not name a concentration camp or ghetto from World War II, and 41 percent could not identify Auschwitz, a network of Nazi concentration and extermination camps.

The study found that the vast majority of respondents support Holocaust education. Ninety-three percent of the respondents said that all students should learn about the Holocaust in school and 80 percent said it was important to educate about the Holocaust to prevent it from happening again. But, 58 percent of respondents believe that “something like the Holocaust could happen again.”

Claims Conference President Julius Berman expressed concern about the lack of knowledge about the Holocaust among millennials.

“We are alarmed that today’s generation lacks some of the basic knowledge about these atrocities,” he said in a statement.

The group’s executive vice president, Greg Schneider, said the study’s findings highlighted the importance of Holocaust education.

“There remain troubling gaps in Holocaust awareness while survivors are still with us; imagine when there are no longer survivors here to tell their stories,” Schneider said. “We must be committed to ensuring the horrors of the Holocaust and the memory of those who suffered so greatly are remembered, told and taught by future generations.”

The study was conducted Feb. 23-27 by Schoen Consulting. It has a margin of error of plus or minus 3 percent