CACAK, Serbia—Three workers sustained light injuries in a strong explosion that rocked an ammunition plant’s facilities in the Serbian town of Cacak on Saturday evening, state RTS television reported. Police blocked access to the factory and ambulances and fire fighters were seen nearby, a Reuters reporter at the site said, adding there was a smell of explosives in the air but no fire could be seen. The mayor of Cacak ordered the evacuation of people living near the factory, RTS reported. The three injured workers were hospitalized. “There was a huge blast, and the house shook under us and then we saw a huge mushroom cloud,” said a man who lives near the factory and identified himself as Milorad, 60. He said he did not want to evacuate. The investigation was under way, the authorities said. This is the second explosion this month at the Sloboda plant, which produces home …