Kissinger also pointed to Iran as a primary challenge, and said that opposing the Islamic republic's "hegemonic expansion" and pursuit of nuclear weapons should remain high Washington priorities.

Kissinger, who at age 94 continues to advise on foreign policy matters, joined two other foreign policy heavyweights -- former secretary of state George Shultz, 97, and ex-deputy secretary of state Richard Armitage, 72 -- in testifying before a Senate panel about global security challenges.

The elder statesmen presented a picture of mounting international threats, including nuclear proliferation, Chinese authoritarianism, and Russia's interference in US elections and its interventions in Eastern Europe.

"The most immediate challenge to international security is posed by the evolution of the North Korea nuclear program," Kissinger told the Senate Armed Services Committee, describing an "unprecedented" scenario.

North Korea, like Iran, has advanced its nuclear capability at the very time an international effort sought to prevent a "radical regime" from developing such capacity.

"For the second time in a decade, an outcome that was widely considered unacceptable is now on the verge of becoming irreversible," he said.

Inability to curb Pyongyang's nuclear efforts could prompt a new arms race in Asia, Kissinger said.

"Denuclearization of North Korea must be a fundamental goal... and if it is not reached, we must prepare ourselves for proliferation of nuclear weapons to other countries," he said.

Kissinger warned against forcing a military confrontation, but said he supported pressure on Pyongyang.

- 'Lack of consistency' -

Armitage criticized President Donald Trump's administration over addressing global threats.

"Unfortunately, the lack of consistency in recent US foreign policy has created uncertainty about America's role in the world," Armitage said.

"We are already seeing concerning signs about the loss of American leadership," he said.

Shultz argued that rapid demographic growth in Africa could trigger mass migrations, a threat that western nations "can't ignore."

But he insisted that the increasing use of technology to miniaturize and automate dangerous weaponry could lead to chaos.

"You have small, cheap and highly lethal replacing large, expensive" weaponry, said Shultz, 97.

That miniaturization is also a key component of Russian and US plans to modernize their respective nuclear arsenals.

The Pentagon is set to unveil Trump's nuclear policy next week, and a leaked draft version indicates that low-yield nuclear weapons could soon be designed for use on the battlefield, rather than to level a city.

Shultz, who reiterated his position supporting the elimination of nuclear weapons, dismissed such tactical bombs as "a mirage."

"It is alarming, this notion that we can have a small nuclear weapon... and that somehow that's usable," Shultz said.

The use of such weapons would rapidly lead to catastrophic escalation, he said.