Washington DC - US President Joe Biden promised a nuclear attack by North Korea would spell "the end" of the regime in Pyongyang, as he hosted South Korean President Yoon Suk-yeol at the White House on Wednesday.

"Look, a nuclear attack by North Korea against the United States or its allies or partners is unacceptable and will result in the end of whatever regime, were it to take such an action," Biden said at a press conference with Yoon in Washington.

The presidents said they were strengthening military cooperation between Washington and Seoul, including more joint training exercises, intelligence sharing, and deployments of strategic US capabilities such as nuclear-armed submarines.

The US has not docked one of its nuclear submarines in South Korea since the 1980s.

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Biden said the steps were being taken to bolster deterrence efforts amid the nuclear threat from North Korea and Pyongyang's escalating aggression.

Yoon said Seoul and Washington would, in the event of a nuclear attack by Pyongyang, "respond swiftly, overwhelmingly, and decisively using the full force of the alliance, including the United States' nuclear weapons."

South Korea is to be given more insight into the US government's strategic planning with regard to nuclear threats. Senior US officials said this was modelled on what Washington did with European allies at the height of the Cold War.

At the same time, South Korea says it is committed to its status as a non-nuclear power.