Vatican City • Pope Francis warned Friday that international relations can no longer be “held captive” by fear-based nuclear deterrence policies and urged government leaders to instead pursue an admittedly utopian future of a world free of atomic weapons.

Francis welcomed Nobel laureates, United Nations officials, NATO representatives and diplomats from countries with the bomb to a Vatican conference aimed at galvanizing global support for complete nuclear disarmament.

The pope acknowledged that current tensions might make a rapid shift away from the Cold War-era idea that nations need nuclear weapons to prevent their enemies from using them “increasingly remote.”

But he said relying on nuclear arsenals to maintain a balance of power “creates nothing but a false sense of security.” Any use of them, even accidental, would be “catastrophic” for humanity and the environment, he warned.

“International relations cannot be held captive to military force, mutual intimidation and the parading of stockpiles of arms,” Francis said. Peace and security among nations must instead be “inspired by an ethics of solidarity,” he said.

The Catholic Church’s first Jesuit and first Latin American pope added that “progress that is both effective and inclusive can achieve the utopia of a world free of deadly instruments of aggression.”

Francis endorsed a new U.N. treaty calling for the elimination of atomic weapons, saying it filled an important gap in international law. Beatrice Fihn, executive director of the International Campaign to Abolish Nuclear Weapons, the advocacy group that won this year’s Nobel Peace Prize for its instrumental role in getting the treaty passed, is among the speakers at the two-day Vatican meeting.

The conference comes amid mounting tensions on the Korean peninsula and heated rhetoric between Washington and Pyongyang over the North’s nuclear ambitions. But the event’s organizer, Cardinal Peter Turkson, told participants that the gathering was planned well before U.S. President Donald Trump began his current trip to Asia, where the Korean nuclear threat has topped his agenda.

Drawing laughs from the largely secular audience, Turkson said it was “divine providence” that the conference and U.S. president’s trip coincided.

The conference is the first major international gathering since 122 countries approved the U.N. nuclear weapons treaty in July. None of the nuclear powers or NATO members signed on to the accord, arguing that its lofty ideals were unrealistic given the rapid expansion of North Korea’s nuclear weapons program and other nuclear threats.

Fihn, head of the Nobel-winning ICAN, said the treaty will have an impact even on the nuclear-armed countries that refused to participate. Previous treaties banning chemical and biological weapons were a crucial first step in making such arsenals illegal, and put pressure on countries that had the weapons to disarm, she said.

“If international law says it’s prohibited, it’s going to make it a lot harder for them (nuclear states) to justify their decisions to modernize and invest in new types of weapons,” she told The Associated Press on the sidelines of the conference.

And if nuclear weapons were to be used, the effects would be devastating for humanity and future generations, Francois Bugnion of the International Committee of the Red Cross warned.

“As the [Red Cross] learned in Hiroshima, there are no effective means of assisting survivors while protecting those delivering assistance,” Bugnion said. “The majority of victims will be denied the medical assistance they need.”

The United States was represented at the conference by its deputy ambassador to the Holy See, Luis Bono, while Russia sent an ambassador and a top nuclear expert, Alexei Arbatov. China and North Korea were invited, but organizers said they didn’t attend. Neither has diplomatic relations with the Holy See.

Bono said he wanted to be there because “we’re interested to hear what the Holy See is saying” about nuclear disarmament. He noted that Trump was in China meeting with President Xi Jinping and trying to find ways to pressure North Korea to abandon its nuclear aspirations.

In his speech, Francis didn’t mention North Korea by name. The Vatican has ruled out — at least publicly — assuming a mediation role in the tense dispute. But Cardinal Turkson told reporters the Vatican was seeking direct contact with the North via the bishops’ conference of South Korea.