Updated

White House Press Secretary Sean Spicer apologized late Tuesday after stating in his daily briefing that Adolf Hitler "didn't even sink to using chemical weapons."

"Today I was trying to describe the attack that [Syrian President Bashar] Assad made on his own people using chemical weapons," Spicer told Fox News. "Frankly, I mistakenly used an inappropriate and insensitive reference to the Holocaust, to which there is frankly no comparison.

"Obviously, that is not what I was intending to do. And I — especially during this week [Passover] — regret using that term and apologize and hope that we can focus on the president's decisive action that he took to make sure that we deal with the situation in Syria."

Spicer was discussing last week's chemical weapons attack, which killed nearly 90 Syrian civilians, when he said "we didn't use chemical weapons in World War II." Spicer later added that "someone as despicable as Hitler ... didn't even sink to using chemical weapons."

After the briefing, Spicer emailed this statement to reporters: "In no way was I 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. Any attack on innocent people is reprehensible and inexcusable."

House Minority Leader Nancy Pelosi, D-Calif., accused Spicer of "downplaying the horror of the Holocaust."

"Sean Spicer must be fired, and the President must immediately disavow his spokesman’s statements," Pelosi said in a statement. "Either he is speaking for the President, or the President should have known better than to hire him."

Rep. Lee Zeldin, R-N.Y., who is Jewish, said in a statement that "as far as comments being made and comparisons of various tactics and methods between now and World War II, you can make the comparison a little differently and it would be accurate, but it's important to clear up that Hitler did in fact use chemical warfare to murder innocent people."

Defense Secretary Jim Mattis touched on the issue at the Pentagon when discussing missile strikes launched by the U.S. against one of Assad's airfields in response to the chemical attack.

"Even in World War II, chemical weapons were not used on battlefields," Mattis said. "Since World War I, there has been an international convention on this. To stand idly by, when that convention is violated, that is what we had to take action on, urgently, in our own vital interest."

Spicer's comments came on the first day of Passover and a day after the White House held a Seder dinner marking the emancipation of the Jewish people, a tradition started during the Obama administration.

According to the U.S. Holocaust Memorial Museum, the Nazis experimented with poison gas in late 1939 with the killing of mental patients, which was termed "euthanasia." Both mobile and stationary gas chambers were later used, with up to 6,000 Jews gassed each day at Auschwitz alone.

On Monday, the White House clarified remarks Spicer made from the podium that the use of barrel bombs by Assad's government might lead to further military action by the United States.

In an exchange with reporters, Spicer appeared to draw a new red line for the Trump administration when he told reporters that if a country gases a baby or it puts "a barrel bomb into innocent people, I think you will see a response from this president."

Until Monday the administration had maintained that last week's airstrikes were in response to the Syrian government's use of chemical weapons against its own citizens. A White House spokesman said later that "nothing has changed in our posture" and the president retains the option to act if it's in the national interest.

Fox News' Serafin Gomez and The Associated Press contributed to this report.