13/04/2017 11:50 AM AEST | Updated 13/04/2017 11:52 AM AEST

Sean Spicer Apologises Again For 'Inexcusable' Adolf Hitler Comments

White House press secretary Sean Spicer has described his comments about Adolf Hitler as "inexcusable and reprehensible", as he again apolgogised for suggesting the Nazis "didn't even sink to using chemical weapons".

Spicer has been under fire since Tuesday's press briefing where he compared the use use of chemical weapons by Syrian President Bashar Assad's regime to the actions of Hitler.

The Nazis gassed millions of Jewish people in concentration camps.

In an interview with MSNBC's Greta Van Susteren on Wednesday, Spicer said he "screwed up" on a "personal and professional" level.

"I should not have tried to make a comparison. There is no comparing atrocities," he said.

Van Susteren began the interview on stage at Washington DC's Newseum by asking Spicer: "Umm. The Holocaust situation, question. Your thoughts today?"

"I made a mistake. There is no other way to say it. I got into a topic I shouldn't have and I screwed up," Spicer said.

"It's a very holy week for both Jewish people and the Christian people and to make a gaffe and mistake is inexcusable and reprehensible. Of all weeks, this compounds that kind of mistake."

Asked if he had spoken to President Donald Trump since the press briefing, Spicer said he had not. "This was my mistake. My bad that I needed to fix," he added. "This was mine to own, mine to apoogise for."

The White House press secretary said Tuesday would "definitely go down as not a very good day in my history".

Spicer also told Van Susteren his comment about Hitler had distracted from President Trump's "unbelievably successful couple of weeks" which saw him launch missile strikes against Assad. "I've let the president down," he said.