WASHINGTON

President Joe Biden issued a grim warning to North Korea Wednesday, saying any nuclear attack from Pyongyang against the US or its partners would lead to its "end."

"A nuclear attack by North Korea against the United States or its allies or our partners is unacceptable, and will result in the end of whatever regime were to take such an action," Biden said in the White House’s Rose Garden alongside South Korean President Yoon Suk Yeol.

The announcement comes as Washington and Seoul announced new bilateral steps known as the "Washington Declaration" in response to North Korea's nuclear and ballistic missile development.

The plan, announced as Yoon is bestowed with an official state visit at the White House, envisages a number of new actions taken by regional partners, including the resumption of US nuclear-armed submarines docking in South Korea for the first time in more than 40 years.

Such visits were terminated in 1991 as the US also pulled its nuclear weapons from the South amid a pact signed that year between the Koreas that pledged joint curtailment of all nuclear-related activities.

But the North's continued development of ballistic missiles and nuclear tests have been in violation of the declaration, as well as successive UN Security Council resolutions, as it seeks to apply pressure on the US to drop economic sanctions.

In addition to the submarine visits, the US and South Korea are also setting up what they are calling a "nuclear consultative group," which will hold regular meetings focused on planning a joint response to a nuclear attack. The body is tasked with reporting to the nations' leaders regularly and the nations will also work to better integrate the South's military with the US' as part of the plans for a joint deterrence against North Korea.

"Our two countries have agreed to immediate bilateral presidential consultations in the event of North Korea's nuclear attack -- a promise to respond swiftly, overwhelmingly and decisively using the full force of the alliance, including the United States' nuclear weapons," said Yoon.

He said the nations "want to customize our response against North Korea's nuclear threats based on extended deterrence."

"In the process of achieving this goal, any concerns that Koreans may have against North Korean nuclear weapons will be relieved, I believe. If nuclear weapons are used, our two countries will strengthen our response in a swift manner," he told reporters.

Biden said the Washington Declaration is a "prudent step to reinforce" the nations' "extended deterrence" in response to North Korea's "escalatory behavior," maintaining the US will not return any nuclear weapons to the Korean Peninsula but will work more closely with Seoul to respond to any potential nuclear strike from the North.

He further emphasized that Seoul has "repeatedly reaffirmed" its commitments under the Nuclear Non-Proliferation Treaty, the landmark 1968 agreement intended to curb the spread of nuclear technology.