The US said Thursday it is still committed to a completely denuclearized Korean Peninsula and that South Korea has made it clear it is not seeking nuclear weapons, a day after President Yoon Suk Yeol openly backed a nuclear buildup if North Korea poses a bigger threat than now.

Yoon’s remarks about South Korea arming itself with nuclear weapons against North Korea, a nuclear state, were made public Wednesday when his defense minister briefed him on the ministry’s plan for this year. Inter-Korean tension is expected to escalate as Pyongyang shows no signs of dialing down its aggression, which reached a peak last year when it conducted an unprecedented number of missile tests.

Yoon’s office responded by saying Yoon had meant “bolstering extended deterrence,” referring to US support involving its nuclear umbrella and strategic assets like bombers and fighters -- all meant to prevent outside aggression, including North Korea, South Korea’s biggest security threat.

The South Korean and US defense chiefs first officially discussed the term at their annual security meeting in October 2006 following North Korea’s first nuclear test that month. Since then, the two allies have routinely reaffirmed the commitment to remind an increasingly belligerent Pyongyang of their superior firepower. And that is not about to change, according to the White House.

“What we are going to seek, jointly together with them, are improvements in extended deterrence capabilities,” White House National Security Council spokesman John Kirby said at a press briefing.

Gen. Pat Ryder, the Pentagon press secretary, struck a similar chord that same day, saying the US seeks denuclearization in the region and that South Korea “falls under that extended deterrence umbrella.” Such US deterrence “has worked very well to date,” Ryder noted without elaborating.

This was the first time a South Korean leader openly floated a nuclear prospect. Former President Park Chung-hee, who was assassinated by his own spy chief in 1979, had to abandon nuclear ambitions in the face of strong opposition from the US.