DAMASCUS—Angrily declaring that the attack would not go unpunished, Syrian leader Bashar al-Assad vowed swift retaliation on his nation’s civilians Friday for the U.S. missile strike on the al-Shayrat air base. “In response to the egregious aggression of the United States, I promise to stop at nothing to crush the Syrian people quickly and decisively,” said Assad, announcing a full-scale military assault on noncombatants in residential neighborhoods throughout Syria that would make the U.S. “sorely regret its unprovoked and criminal deeds.” “This act of war on the part of the United States leaves us no choice but to strike Syrian hospitals, schools, and places of worship with even more force and resolve. Mark my words: the streets of Syria will run red with the blood of civilian men, women, and children, and America will know the price to be paid for its belligerence.” At press time, Russian officials had decried the U.S. missile strike and said they had not ruled out supporting their ally in any counterattack against Syrian civilians.