The Syrian government’s staunch allies strongly condemned the overnight airstrikes on Assad regime targets, with Iran’s supreme leader branding as “criminals” President Donald Trump, U.K. Prime Minister Theresa May and French President Emmanuel Macron.

Russian President Vladimir Putin denounced the attack in a statement Saturday. “With their actions, the U.S. is deepening a humanitarian catastrophe in Syria,” he said, calling for an emergency meeting of the United Nations Security Council to discuss the situation.

But...