Jessica Estepa, and David Jackson

USA TODAY

WASHINGTON — President Trump's spokesman backtracked Tuesday on comments likening Bashar Assad to Holocaust architect Adolf Hitler.

"We didn't use chemical weapons in World War II. You had a ... someone as despicable as Hitler who didn't even sink ... to using chemical weapons," White House Press Secretary Sean Spicer said during Tuesday's press briefing. "You have to, if you're Russia, ask yourself, is this a country and a regime you want to align yourself with?"

Later asked to explain, Spicer said he meant to say that Hitler had not used chemical weapons in battlefield situations as Assad did last week.

"I think when you come to sarin gas... he was not using the gas on his own people the same way that Assad is doing," he said. "He brought them into the Holocaust center, I understand that. But I was saying that in the way that Assad used them, where he went into towns, dropped them down into innocent — into the middle of towns."

Spicer apologized for his comments Tuesday evening, calling them "insensitive." The White House spokesman tried to clarify his comments in an interview with CNN's Wolf Blitzer.

"Frankly, I mistakenly made an inappropriate and insensitive reference to the Holocaust, for which there is no comparison," Spicer said. "And for that I apologize. It was a mistake to do that."

Critics hit Spicer for using the term "Holocaust center" rather than concentration camp, as well as his statement that Hitler did not use gas "on his own people"; many Germans died in the Holocaust.

Spicer clarified what he meant in a statement: "In no way was I trying to lessen the horrendous nature of the Holocaust. However, I was trying to draw a contrast of the tactic of using airplanes to drop chemical weapons on innocent people."

Millions of people died during the Holocaust, with gas chambers being one of the primary ways of killing the victims.

Shortly after Spicer's comments, the U.S. Holocaust Memorial Museum sent out footage of the liberation of the Buchenwald concentration camp.

The Anne Frank Center for Mutual Respect called for Trump to fire Spicer, saying that he was engaging in Holocaust denial.

"On Passover no less, Sean Spicer has engaged in Holocaust denial, the most offensive of fake news imaginable, by denying Hitler gassed millions of Jews to death," Steven Goldstein, the center's executive director, said in a statement. "Spicer's statement is the most evil slur upon a group of people we have ever heard from a White House press secretary."

Joining in the call for the president to fire Spicer: House Minority Leader Nancy Pelosi.

"While Jewish families across America celebrate Passover, the chief spokesman of this White House is downplaying the horror of the Holocaust," the California Democrat said in a statement. "Sean Spicer must be fired, and the president must immediately disavow his spokesman's statements. Either he is speaking for the president, or the president should have known better than to hire him."

Spicer's comments spurred much outrage online, especially given that it is Passover.