Adopting a less confrontational stance than key allies, South Korea's president urged North Korea to abandon its nuclear weapons and seek dialogue to prevent conflict breaking out on the divided peninsula.
President Moon Jae-in voiced support for stronger sanctions in response to the North's recent weapons tests, but his tone was in stark contrast to President Donald Trump's dark warning at the UN General Assembly on Tuesday that North Korea would be "totally destroyed" if it attacked.
Another US ally, Japan, said Wednesday that pressure, not dialogue, was needed.
Moon cautioned that North Korean nuclear issues need to be "managed stably" to prevent a spike in tensions and military clashes - a prospect that has overshadowed this year's gathering of world leaders.
Pyongyang conducted its most powerful underground atomic test explosion and fired missiles over Japan twice in the past three weeks.
The standoff over North Korea's weapons development has intensified as its autocratic leader Kim Jong Un has accelerated his nation's development of a nuclear-tipped missile that could soon strike the continental United States.
Yet it is still South Korea, and its capital Seoul close to the heavily militarised frontier with the North, that faces the greatest immediate risk in a conflict.
"(North Korea) must immediately cease making reckless choices that could lead to its own isolation and downfall and choose the path of dialogue," Moon said.
"We do not desire the collapse of North Korea. We will not seek unification by absorption or artificial means, if North Korea makes a decision even now to stand on the right side of history, we are ready to assist North Korea together with the international community."
