President Donald Trump said on Wednesday that this week's chemical weapons attack in Syria that killed more than 70 people had crossed "many, many lines" and had "changed" his position on President Bashar al-Assad.
"When you kill innocent children, innocent babies — babies, little babies — with a chemical gas that is so lethal, people were shocked to hear what gas it was, that crosses many, many lines," Trump told reporters in the White House Rose Garden while standing next to King Abdullah II of Jordan.
U.S. officials said the gas was likely chlorine, with traces of a nerve agent like sarin, The New York Times reports.
Tuesday's attack, which killed 72 people — including as many as 11 children — "had a big impact on me — big impact," Trump said.
"My attitude towards Syria and Assad has changed very much."
Trump blamed the attack on Assad's forces, despite denials from the Syrian dictator and Russia, saying that the assault has changed his previous reluctance to involve the U.S. in the Middle East.
The change could possibly lead Trump to consider military action or air strikes against Assad, similar to what the Obama administration debated — and declined — after a 2013 chemical weapons attack.
The year before, President Barack Obama had drawn a "red line" — declaring that no such weapons would be allowed, under any circumstances, by Assad's forces.
"I'm not saying I'm doing anything one way or the other," Trump said, adding to the reporter who asked the question: "But I'm certainly not going to be telling you, as much as I respect you."
He reiterated his longstanding claim that Obama had emboldened Assad when he failed to take action after the previous attack.
"I think the Obama administration had a great opportunity to solve this crisis," Trump said. "When he didn't cross that line, after making the threat, I think that set us back a long way.
"It was a blank threat."
Meanwhile, U.N. Ambassador Nikki Haley promised a strong and possibly even unilateral American response.
"When the United Nations consistently fails in its duty to act collectively, there are times in the life of states that we are compelled to take our own action," Haley declared, holding up pictures of children who died in the attack.
The U.S., France and Britain also accused the Syrian government for the attack and slammed Russia for opposing a U.N. Security Council resolution condemning the assault.
Moscow has been Syria's primary ally in the six-year-old civil war.
Since the attack Tuesday in rebel-held territory in northern Syria, Trump has been under increasing pressure to explain whether the assault was egregious enough to force a U.S. response.
After all, Trump's first reaction to the attack was to blame Obama's "weakness" in earlier years for enabling Assad.
"I now have responsibility," Trump said. "That responsibility could be made a lot easier if it was handled years ago."
Though Trump has assigned no blame to Russia or Iran, Assad's two staunchest allies, both Haley and Secretary of State Rex Tillerson have argued adamantly that both must use their influence to prevent Assad from mounting further attacks.
As the Security Council weighed a resolution condemning chemical weapons use in Syria, Haley accused Moscow of blocking action and closing its eyes to the "barbarity" of three previous chemical attacks, also blamed on the Syrian government.
The most recent attack in the town of Khan Sheikhoun bore telltale signs of nerve agent exposure such as victims convulsing and foaming from the mouth.
Videos showed volunteer medics using firehoses to wash chemicals from victims' bodies and lifeless children being piled in heaps.
Early U.S. assessments show the attack most likely involved chlorine and traces of the nerve agent sarin, according to two U.S. officials who weren't authorized to speak publicly about intelligence assessments and demanded anonymity.
Use of sarin would be especially troubling because it would suggest Syria may have cheated on its previous deal to give up chemical weapons.
After the 2013 attack, the U.S. and Russia brokered a deal in which Syria declared its chemical weapons arsenal, agreed to destroy it and join the Chemical Weapons Convention.
Chlorine, which has legitimate uses as well, isn't banned under that convention except when used in a weapon. But nerve agents like sarin are banned in all circumstances.
As Trump and other world leaders scrambled for a response, the U.S. was working to lock down details proving Assad's culpability.
Russia's military, insisting Assad wasn't responsible, has said the chemicals were dispersed when a Syrian military strike hit a facility where the rebels were manufacturing weapons for use in Iraq.
An American review of radar and other assessments showed Syrian aircraft flying in the area at the time of the attack, a U.S. official said. Russian and U.S. coalition aircraft were not there, the official said.
The Associated Press contributed to this report.