President Donald Trump said Monday he will make a decision on how to respond to an apparent chemical weapons attack by the Syrian government in the next 48 hours. And he said another U.S. military strike is possible.

But Trump also told reporters a decision could come later Monday, saying “nothing is off the table” when asked specifically about the possibility he would order a second round of U.S. military strikes in the conflict-torn country in a year.

“We’ll be making that decision very quickly. Probably by the end of today,” he said. “We cannot allow atrocities like that. … It was atrocious. It was horrible. This is about humanity and it can’t be allowed to happen.

“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 told reporters during a Cabinet meeting at the White House.

The U.S. president last year ordered cruise missile strikes on targets in Syria after the country’s president, Bashar al-Assad, ordered a chemical weapons strike that killed civilians. Trump was moved by images of dead children, aides said last year.