The Anne Frank Center for Mutual Respect on Tuesday called for President Donald Trump to fire White House press secretary Sean Spicer “at once” for his comments about Adolf Hitler and chemical weapons.

“On Passover no less, Sean Spicer has engaged in Holocaust denial, the most offensive form of fake news imaginable, by denying Hitler gassed millions of Jews to death,” Steven Goldstein, the executive director of the center, said in a statement.

He called Spicer’s comments “the most evil slur upon a group of people we have ever heard from a White House press secretary.”

“Sean Spicer now lacks the integrity to serve as White House press secretary, and President Trump must fire him at once,” Goldstein said.

During his daily press briefing on Tuesday, Spicer appeared to unfavorably compare Syrian President Bashar Assad to Adolf Hitler while responding to a question about an alleged chemical weapons attack in Syria last week.

“You had a — someone as despicable as Hitler, who didn’t even sink to using chemical weapons,” Spicer said.

Later in the briefing, Spicer tried to clarify by claiming that Hitler “was not using the gas on his own people the same way that Assad is doing.”

Spicer appeared to coin a new euphemism when he said that Hitler brought people into “Holocaust centers” — presumably also known as concentration camps.

His remarks were striking given that Hitler killed millions of Jews, including German citizens, many in gas chambers.

MSNBC noted that in its chyron during Spicer’s remarks.

After the briefing, Spicer issued another three clarifications in quick succession.

Spicer statement: “In no way was I trying to lessen the horrendous nature of the Holocaust, however…” pic.twitter.com/SiBZfgOZZ7 — Bradd Jaffy (@BraddJaffy) April 11, 2017

WH just sent out an updated clarification from Spicer, changing “innocent people” to “population centers” at the end. via @HallieJackson pic.twitter.com/A3k9W75ztt — Bradd Jaffy (@BraddJaffy) April 11, 2017