The Anti-Defamation League (ADL) is offering to host a Holocaust education course for Sean Spicer and his staff after the White House press secretary wrongly claimed that Nazi leader Adolf Hitler did not use chemical weapons during World War II.

“While you have apologized, this week’s incident as well as others (notably the International Holocaust Remembrance Day statement omitting Jews and your vociferous defense of it), have exposed a serious gap in your knowledge of the Holocaust, its impact and the lessons we can learn from it,” ADL CEO Jonathan Greenblatt wrote in a letter to Spicer Thursday.

.@ADL_National has sent a letter to Sean Spicer offering to hold a Holocaust education training session for Spicer and W.H. staffers. pic.twitter.com/hrFsJe3jg6 — Kyle Griffin (@kylegriffin1) April 13, 2017

The White House did not immediately respond to a request for comment.

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The offer comes two days after Spicer caused a furor with his claim about Hitler, which was an attempt to compare the German dictator to Syrian President Bashar Assad, who is accused of using chemical weapons on civilians.

“We did not use chemical weapons in World War II. You had someone as despicable as Hitler who did not even sink to using chemical weapons,” Spicer said during his Tuesday press briefing.

While Hitler is believed not to have used chemical weapons on the battlefield, the Nazis used Zyklon B and other types of poison in gas chambers to kill millions of Jews in concentration camps.

The spokesman apologized for his statement after stumbling over multiple attempts to clarify it.

“Frankly, I mistakenly used an inappropriate and insensitive reference to the Holocaust,” he said during an interview on CNN. “For that I apologize. It was a mistake to do that.”

Spicer said he knew that gas chambers were used to exterminate Jews during the Holocaust.