U.N. Secretary-General Antonio Guterres says the threat from weapons of mass destruction "seems to be gathering force" and is urging expanded diplomatic efforts to tackle the security challenge posed by North Korea's nuclear ambitions.

The U.N. chief told the Security Council on Thursday that the international community must build on the "small signs of hope" from recent contacts between the two Koreas to pursue diplomacy and denuclearize the Korean Peninsula.

Guterres said "global anxieties about nuclear weapons are the highest since the Cold War," and warned of "unimaginable consequences" from "the growing risk of military confrontation."

He also expressed concern at the "ebb" in trust on nuclear and other weapons-related issues between the U.S. and Russia, and the use of chemical weapons in the Syrian conflict.