White House press secretary Sean Spicer has said Adolf Hitler "didn't even sink to using chemical weapons" - a comment at odds with Hitler's extermination of Jews during the Holocaust using gas chambers.

Mr Spicer was attempting to discuss the horror of the chemical weapons attack last week in Syria, which the US administration is blaming on President Bashar Assad.

"We didn't use chemical weapons in World War Two," said Mr Spicer, adding that "someone as despicable as Hitler... didn't even sink to using chemical weapons".

Minutes later, Mr Spicer delivered a garbled defence of his remarks in which he tried to differentiate between Hitler's actions and the gas attack on Syrian civilians last week.

The attack in northern Syria left nearly 90 people dead, and Turkey's health minister said tests show sarin gas was used.

Mr Spicer said: "I think when you come to sarin gas, there was no, he (Hitler) was not using the gas on his own people the same way that Assad is doing.

"There was clearly... I understand your point, thank you. There was not... He brought them into the Holocaust centre (sic), I understand that.

"I appreciate the clarification. That was not the intent."

After the briefing, Mr Spicer emailed a statement to reporters which read: "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."

Mr Spicer's comments came on the second 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 US Holocaust Memorial Museum, the Nazis experimented with poison gas in late 1939 with the killing of mental patients, which was termed "euthanasia".

It is the second day in a row in which Mr Spicer appeared to have trouble articulating US president Donald Trump's foreign policy at a critical time.

The comments came a day after the White House was forced to walk back remarks Mr Spicer made from the podium that the use of barrel bombs by Mr Assad's government might lead to further military action by the US.

In an exchange with reporters on Monday, Mr 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 Trump administration had maintained that last week's air strikes 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 is in the national interest.