April 26, 2017 0535 GMT
While intensifying his criticism of the Syrian leader during a press briefing on Tuesday, Spicer suggested that President Assad was guilty of acts worse than Hitler’s atrocities and asserted that the former chancellor of Germany had not used chemical weapons during World War II.
"You had someone as despicable as Hitler who didn't even sink to using chemical weapons," the White House spokesman said, ignoring the use of gas chambers at concentration camps during the Holocaust.
The generally accepted position asserts that six million European Jews were killed by the Nazis and their World War II collaborators, but some revisionist historians dispute the six million figure, insisting it is massively exaggerated.
Spicer's comments drew an intense backlash from Jewish circles in the United States and some even demanded his resignation.
A few hours later, a subdued Spicer appeared on CNN and apologized for comparing the Syrian leader with Hitler.
"Frankly, I mistakenly used an inappropriate and insensitive comment about the Holocaust and there is no comparison," he stated.
"For that I apologize. It was a mistake to do that,” he added.
Secretary Spicer's apology quite clearly seems to be directed at appeasing his Jewish critics rather than at correcting his unsubstantiated allegations against President Assad, who has been facing a US-led proxy war against his government since 2011.
In recent months, the Syrian army, backed by the Russian air power, has been making major gains against foreign-sponsored terrorist groups, recapturing several strategic areas from their grip, particularly in the strategic northern province of Aleppo.
Two US Navy destroyers fired 59 Tomahawk cruise missiles from the Mediterranean Sea at al-Shayrat airbase in Homs province in western Syria on April 7.
US President Donald Trump said he had ordered the strike in response to the April 4 chemical attack in the Arab country that he blamed on the Syrian government.
The US military claimed the airfield targeted was used to store chemical weapons and Syrian aircraft notwithstanding that Damascus volunteered to destroy its chemical stockpile in 2014 following an agreement which was brokered by the US and Russia.