President Biden on Wednesday warned North Korea that a nuclear attack against the U.S. or its allies would be "the end" of the communist regime.
At a joint press conference with South Korean President Yoon Suk Yeol, Biden was asked about new nuclear deterrence commitments the United States has made to protect South Korea from its hostile neighbor to the north.
"Look, a nuclear attack by North Korea against the United States or its allies, or partisans, or partners is unacceptable and will result in the end of whatever regime were to take such an action," Biden said.
In recent months, North Korea has taken several aggressive actions, including ballistic missile tests and, for the first time, testing a solid-fuel intercontinental ballistic missile earlier this month. The recent test is seen as a possible breakthrough in the North’s efforts to acquire a more powerful, harder-to-detect weapon targeting the continental United States.
Biden called North Korea's actions "escalatory behavior."
In response, the Biden and Yoon have signed an agreement that will permit the U.S. to dock nuclear submarines in South Korea for the first time in more than 40 years.
"Our mutual defense treaty is ironclad, and that includes our commitment to extended deterrence and that includes the nuclear threat and the nuclear deterrent. They are particularly important in the face of DPRK's increased threats and the blatant violation of U.S. sanctions," Biden said Wednesday.
"At the same time, we continue to seek serious and substantial diplomatic breakthroughs with the DPRK to bolster stability on the peninsula, reduce the threat of proliferation, and address our humanitarian and human rights concerns for the people of the DPRK," he added.
The decision to dock nuclear submarines in South Korea is part of a policy rollout occasionally referred to as the "Washington Declaration" — an international positioning of the U.S. to quell growing aggression from communist North Korea.
Yoon, who first entered politics only two years ago to run for president of the Republic of Korea (ROK), is making a state visit to the U.S. with first lady Kim Keon Hee to commemorate the 70th anniversary of the U.S.-South Korea alliance.
On Thursday, Yoon is expected to deliver a speech at a joint session of Congress, making him the first South Korean president to do so in a decade, according to The Washington Post.
In remarks, Yoon said the U.S.-South Korean alliance is a "righteous alliance that contributes to world peace and prosperity."
"Our two leaders have decided to significantly strengthen extended deterrence of our two countries against North Korea's nuclear and missile threats so that we can achieve piece through the superiority of overwhelming forces and not a false peace based on the goodwill of the other side," Yoon said.
Fox News' Timothy H.J. Nerozzi and The Associated Press contributed to this report.