The U.S. launched at least 50 Tomahawk missiles at a Syrian air base late Thursday.
The missiles were reportedly launched from two U.S. Navy destroyers in the Mediterranean Sea and targeted a regime air base in Homs.
Syrian state TV called the strikes an act of "American aggression."
The strikes come after a major chemical weapons attack killed over 80 people near the Syrian town of Idlib. The Trump administration says Syrian President Bashar al-Assad is responsible for the attack.
President Trump said to reporters: "Years of previous attempts at changing Assad's behavior have all failed and failed very dramatically. ... Tonight, I call on all civilized nations to join us in seeking to end the slaughter and bloodshed in Syria."