onsaid he would decide the U.S. response to the “heinous” chemical weapons attack in Syria “over the next 24 to 48 hours.”

“It was an atrocious attack. It was horrible,” Trump told reporters during a Cabinet meeting at the White House. “This is about humanity and it can’t be allowed to happen.”

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The comments were Trump’s first in-person condemnation of the attack, which reportedly killed at least 40 people in a town controlled by opponents of Syrian President Bashar Assad.

After saying it could take as long as two days to decide a U.S. response, Trump later added a decision would come “probably by the end of today.”

The president said he plans to meet with his national security team and military brass later Monday to determine who is responsible and form a retaliation plan.

“If it’s the Russians, if it’s Syria, if it’s Iran, if it’s all of them together, we’ll figure it out,” he said.

Trump added that Russian President Vladimir Putin, Assad’s most prominent foreign ally, “may” share responsibility for the attack.

“Everybody is going to pay a price. He will, everybody will,” said the president, who has previously been reluctant to criticize Putin by name.

The reported chemical attack drew international condemnation and signs of a response were already underway early Monday .

The Syrian and Russian governments blamed Israel for an airstrike on a military base that reportedly killed 14 people. Israel has not claimed responsibility for the attack.

The United Nations Security Council was set to meet Monday to discuss an international response.

In April 2017, Trump launched a barrage of cruise missiles at a Syrian air base after pro-Assad forces carried out a chemical attack that killed more than 80 people.

Updated at 12:29 p.m.