WASHINGTON—The U.S. military launched nearly 60 Tomahawk cruise missiles against a Syrian air base Friday, responding to mounting calls for a display of force in the wake of this week’s suspected chemical-weapons attack in Syria.

The strikes represented the first time a U.S. military operation deliberately targeted the regime of President Bashar al-Assad and came a day after U.S. President Donald Trump said the chemical attack in Idlib province on Tuesday had changed his thinking on Syria and Mr. Assad.

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