The Yad Vashem holocaust memorial center on Wednesday urged White House press secretary Sean Spicer to visit its website after his comments on Hitler sparked outrage.

Spicer apologised Tuesday for "insensitive" remarks in which he asserted that unlike the Syrian regime, Adolf Hitler did not use chemical weapons.

Yad Vashem expressed "deep concern regarding the inaccurate and insensitive use of terms related to the Holocaust by the White House press secretary".

"His statements imply a profound lack of knowledge of events of the Second World War, including the Holocaust. Moreover, they are liable to strengthen the hands of those whose goal is to distort history," it said.

The Jerusalem-based center urged Spicer to visit its website to learn more. Yad Vashem is among the world's foremost Holocaust education, documentation and research centers.

During a White House briefing on Tuesday, Spicer sought to intensify criticism of Syrian President Bashar al-Assad, describing his suspected use of sarin nerve gas against civilians last week as historically evil.

"You had someone as despicable as Hitler who didn't even sink to using chemical weapons," Spicer said, momentarily forgetting the Holocaust and prompting outraged calls for his resignation.

A few hours later, a contrite Spicer appeared on US television to apologize for the comments, which coincided with the Jewish holiday of Passover.

Israeli Transport and Intelligence Minister Yisrael Katz initially called Spicer's comments "serious" and "revolting", adding that Israel should demand he apologize or resign.

Katz later told Israel Radio that he accepted Spicer's apology.

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