CARACAS, Venezuela—Nationwide protests are spreading beyond President Nicolás Maduro’s control and risk morphing into civil war, said a retired Venezuelan general who was in charge of suppressing the last wave of unrest three years ago.

“We’re seeing much larger masses protesting across all major cities, including the working-class neighborhoods” once firmly supporting the government, said Major Gen. (Ret.) Miguel Rodríguez Torres, who served as Mr. Maduro’s interior minister in 2013 and 2014. “The government is losing control.”

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