NEW YORK (CBSNewYork) — White House Press Secretary Sean Spicer issued a full apology Tuesday, after drawing ire on social media upon saying Adolf Hitler “didn’t even sink to using chemical weapons” in World War II.

Spicer made the comments during his daily press briefing Tuesday, when a reporter asked him about the future of Russia’s alliance with the Assad regime following last week’s deadly chemical attack in Syria.

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“We didn’t use chemical weapons in World War II, you had someone as despicable as Hitler who didn’t even sink to using chemical weapons,” Spicer said, comparing Hitler to Syrian President Bashar al-Assad. “So you have to, if you’re Russia, ask yourself is this a country that you and a regime that you want to align yourself with.”

Later in his briefing, Spicer tried to clarify his remarks.

“I think when you come to Sarin gas, he (Hitler) was not using the gas on his own people the same way that Assad is doing,” Spicer said. “He brought them into the Holocaust center, I understand that. But I’m saying in the way that Assad used them, where he went into towns, dropped them down into the middle of towns.”

The “Holocaust centers” remark apparently meant concentration camps – where millions of Jews and others were murdered.

Following the press conference, the Spicer issued the following statement:

“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.”

He added in an interview: “It was a mistake. I shouldn’t have done it. I won’t do it again.”

As CBS2’s Tony Aiello reported, the comments drew a backlash particularly because they came at the start of Passover.

Spicer’s comments received a lot of backlash on Twitter, with many users citing the use of gas chambers to kill Jews and others in concentration camps.

The Anne Frank Center for Mutual Respect also issued a statement, calling on Spicer to be fired.

Spicer’s comments were also condemned by House Democratic Leader Nancy Pelosi, who called on President Donald Trump to fire Spicer.

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“Frankly I mistakenly used an inappropriate and insensitive reference to the Holocaust, which frankly there is no comparison,” Spicer said. “For that I apologize. It was a mistake to do that.”

Also Tuesday, Trump met with chief executive officers and Cabinet secretaries to talk about job creation.

Meanwhile, the Pentagon held its first media briefing since President Trump ordered last week’s missile strike on the Syrian air base. Secretary of Defense James Mattis said they decided a measured military response could best deter the Assad regime from using chemical weapons again.

“This military action demonstrates the United States will not passively stand by while Assad blithely ignores international law and employs chemical weapons he had declared destroyed,” Mattis said.

All of this comes as Rex Tillerson makes his first trip to Russia as Secretary of State.

“Russia has really aligned itself with the Assad regime, the Iranians and Hezbollah,” Tillerson said. Is that a long-term alliance that serves Russia’s interest?”

Attorney General Jeff Sessions also made his own trip Tuesday to the U.S.-Mexico border in Arizona. He announced new guidelines to crack down on illegal immigration.

He said last month there was a 72 percent drop in illegal border crossings, compared to the month before Trump’s inauguration.

In other developments, the Washington Post reported the FBI got a warrant from a special court to monitor Carter Page, a New York investment banker who advised the Trump campaign last summer.

The Post said the application for the warrant laid out why investigations believed Page “knowingly engaged in clandestine activities on behalf of Moscow.”

Page has repeatedly denied any wrongdoing.

There was also a sigh of relief at the White House as Republican Ron Estes won the special election for an open congressional seat in Kansas.

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His margin of victory was 6 percent in a district President Trump carried by 27 points.