TOKYO — Every year in early August, Japanese politicians and peace activists converge on Hiroshima to commemorate the day when the city was devastated by an American atomic bomb. In the famous peace park, the horrors of World War II are vividly recounted. Speakers of all political stripes repeat Japan’s postwar mantra: “Never again.”

The familiar reaffirmations of peace were there this year, too, on the 72nd anniversary, with Prime Minister Shinzo Abe on Sunday declaring that Japan, “as the only country to be irradiated in war,” would “firmly advance the movement toward a world without nuclear weapons.”

But there was no hiding the tensions straining Japan’s postwar pacifism, as fears over the fast-advancing nuclear program in neighboring North Korea — and political disagreements over how to respond — rose jarringly to the surface.