Officials in US President Joe Biden's administration have begun emphasising the "denuclearisation of North Korea", rather than the whole peninsula, in a subtle but noticeable shift from wording in previous talks with Pyongyang.
In speeches, policy documents, and other communications, senior leaders including Secretary of State Antony Blinken have regularly adopted the phrase in a break from the "denuclearisation of the Korean peninsula".
The "peninsula" wording has been used for a decade in many United Nations Security Council resolutions and international agreements, including the declaration signed by North Korean leader Kim Jong-un and former US President Donald Trump in Singapore in 2018.
Blinken did not respond to a question about the wording during a briefing in Seoul on Thursday, but his South Korean counterpart, Foreign Minister Chung Eui-yong said emphasising the peninsula was "more correct", highlighting a possible point of difference between the two allies.
"It means that to North Korea we are showing that South Korea has already denuclearised ... that we have to go along together," Chung said.
"If we can say 'denuclearisation of the Korean Peninsula,' we are more confident that we can convince North Korea to follow our suit."
The night before, South Korea's Ministry of Defence said the allies had "reaffirmed the common goal of denuclearising the Korean Peninsula", while the Pentagon said they "noted a commitment to supporting diplomatic efforts to achieve the denuclearisation of North Korea."
The US change in wording has not been universal, with Secretary of Defence Lloyd Austin using both phrases during his visit to Seoul with Blinken this week.
But experts and Western diplomatic sources said the new emphasis is deliberate and will be noted.
"On an issue where words are carefully parsed, this is a noticeable shift from 'denuclearisation of the Korean Peninsula' which was the norm in the Obama years," Ben Rhodes, who served as Deputy National Security Advisor under former President Barack Obama, said on Twitter.
Implications of unilateral denuclearisation are "a nonstarter for Pyongyang and is unlikely to jumpstart any negotiations," said Vipin Narang, a nuclear affairs expert at the Massachusetts Institute of Technology in the United States.
"The formulation 'denuclearisation of North Korea' implies unilateral obligations on North Korea - something it has never agreed to, and neither have we," he said.
In a statement on Thursday, a senior North Korean diplomat blasted the Biden administration's talk of complete denuclearisation as a "lunatic theory" that needed to be dropped before talks could resume.
Conflicting or vague views of what denuclearisation means have complicated negotiations that have largely been stalled since 2019.
In 2018, North Korea defined "denuclearisation of the Korean Peninsula" as "removing all elements of nuclear threats from the areas of both the north and the south of Korea and also from surrounding areas from where the Korean peninsula is targeted."
That has been interpreted as the United States withdrawing its troops from South Korea and ending its "nuclear umbrella" security alliance with Seoul, among other conditions.
Washington, meanwhile, has insisted on complete, verifiable, and irreversible dismantling of North Korea's nuclear weapons and the facilities needed to build them. The United States has never publicly said it would reduce its own military presence in return, and regularly stresses its commitment to defending South Korea.
Duyeon Kim, with the US-based Centre for a New American Security, said the wording around denuclearisation is only a big deal if Pyongyang makes it an issue.
"It would be silly and a missed opportunity for Pyongyang if phraseology on denuclearisation in American public comments and statements became deal breakers before any meaningful talks even take place with the Biden administration," she said.