CIUDAD VICTORIA, Mexico—Gunmen aboard a number of vehicles staged attacks in several neighborhoods in the Mexican border city of Reynosa on Saturday, and at least 15 people died in clashes that caused widespread panic, according to local law enforcement. The Tamaulipas state agency coordinating security forces said in a statement that the attacks began in the early afternoon in several neighborhoods in the eastern part of the city, which borders McAllen, Texas. The agency said one person died during an attack on police near a border bridge, but it was not clear if the others were shot in random attacks or were targeted. The shootings mobilized the army, National Guard, state police and other agencies. Authorities said they detained a person who had two women, apparently kidnapped, in the trunk of his car, and said they seized three vehicles. Reynosa Mayor Maki Esther Ortiz Domínguez sent a tweet demanding the …