NAGASAKI, Japan — Visiting the two Japanese cities razed by atomic bombs during World War II, Pope Francis called Sunday for a “world without nuclear weapons,” which he said are “immoral” for war or deterrence.

“We will be judged on this,” Francis said.

In Hiroshima, the pope met with bomb survivors and spoke vividly of the “black hole of death and destruction” that atomic weapons could cause. Earlier, in a somber address in Nagasaki delivered in driving rain, he spoke about the weapons in policy terms and expressed concern that a “climate of distrust” was endangering international arms control efforts.

“Peace and international stability are incompatible with attempts to build upon the fear of mutual destruction,” the pope said in Nagasaki, standing next to an enlarged black and white photograph from the bombing’s aftermath that shows a Japanese boy carrying his dead younger brother on his back.

Francis used the first papal trip to Japan since 1981 to emphasize one of his signature issues in cities that remain lasting symbols of atomic destruction (although both have been fully rebuilt in the decades since the 1945 attacks). The two bombs, dropped three days apart, killed as many as 200,000 people, melted roof tiles and caused skin burns on people who were three miles away from the points of impact.

After laying a wreath to the Nagasaki bombing’s victims, the pope said the arms race creates a false sense of security, poisoning international relationships. He described nuclear weapons as wasteful and environmentally damaging.

“In a world where millions of children and families live in inhumane conditions, the money that is squandered and the fortunes made through the manufacture, upgrading, maintenance and sale of evermore destructive weapons are an affront crying out to heaven,” Francis said.

By saying that nuclear weapons should not be stockpiled for deterrence — a stance he first outlined in 2017 — Francis has gone further than his predecessors. The only other pope to visit Japan, John Paul II, said during the Cold War that deterrence could be “morally acceptable,” so long as it was a step toward disarmament.

The antinuclear message is the centerpiece of the pope’s three-day trip to Japan, the second half of a journey that began in Thailand. Francis paid homage Sunday at a monument dedicated to 26 Christians, a mix of Japanese and foreigners, who were killed in 1597 — an event that signaled the bloody start of more than 250 years of persecution of Christians by Japanese rulers. Today, Catholics make up 0.4 percent of the country’s population.

On Monday, Francis was scheduled to meet in Tokyo with survivors from the country’s 2011 triple disaster in which a 9.0-magnitude earthquake triggered a massive tsunami and meltdowns at a coastal nuclear plant.

His trip to Japan comes amid long standoffs over nuclear programs in Iran and North Korea and little progress in international arms control negotiations. In August, the Trump administration pulled the United States out of a Cold War-era nonproliferation pact, citing complaints that Moscow was not complying — a step that some analysts say could raise the possibility for an arms race. Most major countries, including the United States, have not signed a United Nations treaty that envisions the eventual elimination of nuclear arms.

Japan, citing the protection it receives from the U.S. nuclear umbrella, has also declined to sign that treaty, to the consternation of many bomb victims. The mayors of Nagasaki and Hiroshima have called on Japanese Prime Minister Shinzo Abe to reconsider that stance. Japan’s Catholic bishops have called for the abolition of nuclear arms.

“We must never grow weary of working to support the principal international legal instruments of nuclear disarmament and nonproliferation, including the treaty on the prohibition of nuclear weapons,” Francis said.

For those who have advocated against nuclear weapons, the pope’s address was welcome.

“It was just what I was hoping to hear from him,” said Kazuya Okubo, head of the Nagasaki City Peace and Atomic Bomb museum.

In Hiroshima, Francis heard testimony from an atomic bomb survivor who was 14 years old and working at a factory at the time. The factory collapsed, and she found herself buried under timber and tiles. When she made it out, she said, she saw fire and smelled what she described as “rotten fish.”

“There were people walking side by side like ghosts,” Yoshiko Kajimoto said, “people whose whole body was so burned that I could not tell the difference between men and women, their hair standing on end, their faces swollen to double size, their lips hanging loose, with both hands held out with burned skin hanging from them.

“No one in this world can imagine such a scene of hell.”

Kajimoto said that her father died 1 ½ years later, vomiting blood. Her mother died after 20 years of “suffering.” Kajimoto said she has had many problems of her own: cancer, surgery to remove two-thirds of her stomach. Most of her friends, she said, have died of cancer.

Francis listened to the remarks quietly from his papal chair.

“I work hard to bear witness that we must not use such terrible atomic bombs again nor let anyone in the world endure such suffering,” Kajimoto said.

Harlan reported from Rome.