The U.N. chief said Thursday he is "deeply concerned" by the cancellation of the planned summit between U.S. President Donald Trump and North Korean Leader Kim Jong Un.

Antonio Guterres told an audience at the University of Geneva that he was urging the parties to keep working "to find a path to the peaceful and verifiable denuclearization of the Korean Peninsula."

Guterres' comments came as he laid out his disarmament agenda Thursday, warning that nuclear agreements between states are threatened like never before.

He said nuclear powers must do more to promote disarmament, putting a particular onus on Russia and the United States to remedy a world "going backwards" in this area since right after the Cold War.

He welcomed efforts by the European Union and others to stick to the nuclear deal with Iran that Washington has abandoned.

Guterres' plan offers broad ambitions, from curbing growth in conventional weapons to addressing the prospect of artificial intelligence in war machines. He announced he was launching a new initiative to combat the illicit circulation and trade in small arms within countries and across borders.

"Disarmament concerns every country, and all weapons, from hand grenades to H-bombs," he said. "Deadly weapons put us all at risk and leaders have a responsibility to minimize that risk."

While Guterres said all nuclear-armed states have "primary responsibility" for disarmament and nonproliferation efforts, he called on the U.S. and Russia to end a dispute over the Intermediate-Range Nuclear Forces Treaty, to extend the New START treaty on strategic, offensive weapons, and to do more to cut their nuclear stockpiles.

He noted there are no bilateral talks between Moscow and Washington right now on greater nuclear-arms reductions.

He bemoaned the expansionist ambitions of arms traders, rising military weapons production and the buildup of "massive stockpiles" of conventional weapons — especially in conflict-prone zones.

He said the "total elimination" of nuclear weapons remains the U.N.'s top priority on disarmament, but efforts toward that goal are in "severe crisis."

Since the immediate aftermath of the Cold War, when deals reduced nuclear arsenals and banned nuclear testing, "our world is going backwards," he said.