White House press secretary Sean Spicer said Tuesday that Adolf Hitler didn't use chemical weapons — a comment at odds with Hitler's extermination of Jews during the Holocaust using gas chambers.

Spicer was attempting to discuss the horror of the chemical weapons attack last week in Syria that the U.S. administration is blaming on President Bashar al-Assad.

"We didn't use chemical weapons in World War II," said Spicer, adding that "someone as despicable as Hitler ... didn't even sink to using chemical weapons."

Someone as despicable as Hitler ... didn't even sink to using chemical weapons. - Sean Spicer , White House press secretary

Minutes later, Spicer delivered a garbled defence of his remarks in which he tried to differentiate between Hitler's actions and the gas attack last week on Syrian civilians. The attack in northern Syria left nearly 90 people dead, and Turkey's health minister said tests show sarin gas was used.

"I think when you come to sarin gas, there was no, he [Hitler] was not using the gas on his own people the same way that Assad is doing," Spicer said. "There was clearly … I understand your point, thank you. There was not … He brought them into the Holocaust centre, I understand that.

"I appreciate the clarification. That was not the intent," he said.

'Most evil slur'

The U.S.-based Anne Frank Center for Mutual Respect issued a statement calling Spicer's comments "the most evil slur upon a group of people" and demanding that Spicer be fired immediately.

.<a href="https://twitter.com/POTUS">@POTUS</a> <a href="https://twitter.com/realDonaldTrump">@realDonaldTrump</a> MUST FIRE SEAN SPICER NOW FOR ENGAGING IN HOLOCAUST DENIAL. OUR STATEMENT BELOW. <a href="https://twitter.com/hashtag/Antisemitism?src=hash">#Antisemitism</a> <a href="https://twitter.com/hashtag/NeverAgain?src=hash">#NeverAgain</a> <a href="https://t.co/4dB9ESCaZr">pic.twitter.com/4dB9ESCaZr</a> —@AnneFrankCenter

After Tuesday's briefing, Spicer emailed a statement to reporters: "In no way was I trying to lessen the horrendous nature of the Holocaust. I was trying to draw a distinction of the tactic of using airplanes to drop chemical weapons on population centres. Any attack on innocent people is reprehensible and inexcusable."

Spicer's comments came on the first day of Passover and a day after the White House held a Seder dinner marking the emancipation of the Jewish people, a tradition started during the Obama administration.

According to the U.S. Holocaust Memorial Museum, the Nazis experimented with poison gas in late 1939 with the killing of mental patients, which was termed "euthanasia."

Spicer's comments drew heavy backlash on social media, including from Chelsea Clinton, the daughter of former U.S. president Bill Clinton and former presidential candidate Hillary Clinton.

I hope <a href="https://twitter.com/PressSec">@PressSec</a> takes time to visit <a href="https://twitter.com/HolocaustMuseum">@HolocaustMuseum</a>. It's a few blocks away. <a href="https://t.co/24fNoMUyS8">https://t.co/24fNoMUyS8</a> —@ChelseaClinton

Someone get <a href="https://twitter.com/PressSec">@PressSec</a> a refresher history course on Hitler stat <a href="https://twitter.com/hashtag/Icantbelievehereallysaidthat?src=hash">#Icantbelievehereallysaidthat</a> —@SenatorCardin

.<a href="https://twitter.com/realDonaldTrump">@realDonaldTrump</a>, it’s time to fire <a href="https://twitter.com/PressSec">@PressSec</a> Sean Spicer. <a href="https://t.co/35sTqfkp1d">https://t.co/35sTqfkp1d</a> <a href="https://t.co/Lw73GVtKDh">pic.twitter.com/Lw73GVtKDh</a> —@NancyPelosi

Spicer later apologized during an interview with CNN, saying he mistakenly used "an inappropriate, insensitive reference to the Holocaust."

"It was my blunder," he said.

It's not the first time the Trump administration has been criticized for comments related to the Holocaust and anti-Semitism.

The White House released a statement on international Holocaust Remembrance Day earlier this year that omitted any mention of Jewish victims.

At the time, Spicer defended that statement by saying it had been written in part by a Jewish staff member whose family members had survived the Holocaust.