White House spokesman Sean Spicer says he is personally and professionally pained by his comments comparing the atrocities of Syrian President Bashar al-Assad and Adolf Hitler, saying made a mistake and let down the President.
His comments were made at a press conference during a discussion on chemical weapons attacks on Syrian civilians blamed on Syrian President Bashar al-Assad.
"You had someone as despicable as Hitler who didn't even sink to using chemical weapons," Mr Spicer said, to gasps of disbelief.
"So you have to, if you are Russia, ask yourself: is this a country and a regime that you want to align yourself with?"
The Nazis are infamous for using gas chambers to exterminate Jews and others in the Holocaust.
"I made a mistake," Mr Spicer said during an event at a museum in Washington on Wednesday.
"There's no other way to say it. I got into a topic that I shouldn't have and I screwed up. I hope I showed that I understand that I did that and that sought people's forgiveness because I screwed up."
Mr Spicer said his comments were professionally upsetting because President Donald Trump had had "an unbelievably successful couple of weeks" and it was his job to amplify that message of accomplishment but "I've let the President down".
His gaffe came on the first day of Passover, which marks the liberation of the Jewish people from Egyptian slavery.
He'd earlier made an apology on CNN.
Reuters / Newshub.