White House press secretary Sean Spicer issued an apology on CNN Tuesday evening after drawing ire over comments he made while comparing Syrian President Bashar Assad with Nazi leader Adolf Hitler.

“I realized that I made a mistake and I don’t want to be a distraction to the president’s agenda," Spicer said during an on-air interview with CNN's Wolf Blitzer. "It was a mistake. I shouldn't have done it. I won't do it again."

During a press briefing earlier Tuesday about the Syrian government's apparent April 4 gas attack that killed dozens of its civilians, Spicer said Hitler "didn’t even sink to using chemical weapons" during World War II. In fact, Hitler's Nazi Germany used poisonous gas, among other methods, to kill 6 million Jewish people during the Holocaust.

“…Look we didn’t use chemical weapons in World War II. You had someone as despicable as Hitler, who didn’t even sink to using chemical weapons,” Spicer said. “You have to, if you’re Russia, ask yourself, 'Is this is a country that you -- and a regime that you -- want to align yourself with?' ”

Spicer made the comparison while discussing how U.S. relations with Russia may be impacted by President Donald Trump’s decision to bomb a Syrian government air base last week.

The comments drew immediate condemnation on Twitter, and the Anne Frank Center for Mutual Respect called for his firing.

".@POTUS @realDonaldTrump MUST FIRE SEAN SPICER NOW FOR ENGAGING IN HOLOCAUST DENIAL. OUR STATEMENT BELOW. #Antisemitism #NeverAgain," the Manhattan-based organization tweeted along with a statement. 

Former first daughter Chelsea Clinton also weighed in on the matter, suggesting Spicer visit the U.S. Holocaust Memorial Museum, which is just "a few blocks away" from the White House.

When reporters asked him to clarify, Spicer said Hitler was not "using gas on his own people the same way that Assad is doing."

“He brought them into the Holocaust centers," Spicer added, apparently referring to concentration camps, before adding that Assad had dropped chemical weapons "in the middle of towns."

After the briefing, Spicer released another statement, saying he was in no way "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 centers," Spicer said in the statement. "Any attack on innocent people is reprehensible and inexcusable."

Spicer's explanation, however, was not sufficient enough for some New York politicians, including Brooklyn Borough President Eric Adams, who called for his resignation as press secretary.

"This callously thoughtless remark is a slap in the face to the memory of every man, woman, and child who was murdered in gas chambers at Nazi concentration camps," Adams said in an emailed statement. "We expect and deserve more from the Trump administration than a series of ‘mistakes’ that have publicly disrespected a group of Americans who have suffered atrocities we can never fully understand."

Spicer's blunder on Tuesday wasn't the first time the Trump administration has seen controversy over the Holocaust. In January, on International Holocaust Remembrance Day, the White House issued a statement that failed to mention Jews, instead opting for the phrase “innocent people.”

“It is with a heavy heart and somber mind that we remember and honor the victims, survivors, heroes of the Holocaust. It is impossible to fully fathom the depravity and horror inflicted on innocent people by Nazi terror,” the Jan. 27 statement from the president read.