The United States fired a barrage of cruise missiles into Syria Thursday night in retaliation for this week’s gruesome chemical weapons attack against civilians, U.S. officials said. It was the first direct American assault on the Syrian government and Donald Trump‘s most dramatic military order since becoming president.

The surprise strike marked a striking reversal for Trump, who warned as a candidate against the U.S. getting pulled into the Syrian civil war, now in its seventh year. But the president appeared moved by the photos of children killed in the chemical attack, calling it a “disgrace to humanity” that crossed “a lot of lines.”

About 60 U.S. Tomahawk missiles, fired from warships in the Mediterranean Sea, targeted an air base in retaliation for a chemical weapons attack that American officials believe Syrian government aircraft launched with a nerve agent, possibly sarin.

The president did not announce the attacks in advance, though he and other national security officials ratcheted up their warnings to the Syrian government throughout the day Thursday.

“I think what happened in Syria is one of the truly egregious crimes and shouldn’t have happened and it shouldn’t be allowed to happen,” Trump told reporters traveling on Air Force One to Florida, where he was holding a two-day summit with Chinese President Xi Jinping.

The strike came as Trump was hosting Xi in meetings focused in part on another pressing U.S. security dilemma: North Korea’s nuclear program. Trump’s actions in Syria could signal to China that the new president isn’t afraid of unilateral military steps. even if key nations like China are standing in the way.