The purported difference came as South Korea is seeking a greater U.S. security commitment after North Korea's record number of missile tests and escalating nuclear doctrine last year caused security jitters among many people in the South.

Some experts say South Korea's statement on the discussion is likely largely based on an agreement between their defence chiefs in November to conduct table-top exercises, usually computer simulations, annually and further strengthen the alliance's information sharing, joint planning and execution. In November, they also reaffirmed the U.S. commitment to providing extended deterrence, a reference to a U.S. promise to use full U.S. capabilities, including nuclear, to protect its allies.

In a newspaper interview published Monday, South Korean President Yoon Suk Yeol said that Seoul and Washington were pushing for joint planning and training involving U.S. nuclear assets and that the United States responded positively to the idea. Asked by a reporter later at the White House about whether the two countries were discussing joint nuclear exercises, Biden replied, “No.”?

After Biden's comments created a brief stir in South Korea, Yoon's top adviser for press affairs, Kim Eun-hye, issued a statement Tuesday to reconfirm Yoon's earlier remarks. Kim said the two countries “are discussing an intel-sharing, a joint planning and subsequent joint execution plans over the management of U.S. nuclear assets in response to North Korea's nuclear (threats).”?

The White House National Security Council in a statement on Tuesday said Biden and Yoon have “tasked their teams to plan for an effective coordinated response to a range of scenarios, including nuclear use by North Korea.”?

A senior Biden administration official said U.S. and South Korean officials are expected to hold table-top exercises soon to chart out a potential joint response to a range of scenarios, including deployment of a nuclear weapon by the North. The official spoke on the condition of anonymity to discuss planning.

Moon Seong Mook, an analyst for the Seoul-based Korea Research Institute for National Strategy, said Yoon likely was referring to the November agreement on the alliance's capabilities, which he said definitely include U.S. nuclear assets that are essential to the U.S. extended deterrence commitment.?

“South Korea isn't a nuclear state so it won't be likely South Korea jointly using U.S. nuclear weapons. But the wording (in the November agreement) meant that South and the U.S. would consult on the operations of U.S. nukes from the planning stage until the training stage,” said Moon, a retired brigadier general.?

While some observers say Yoon's comments to the Chosun Ilbo newspaper didn't reveal much new development on the issue, Moon said that Yoon might have tried to emphasize efforts to boost the effectiveness of the U.S. extended deterrence because North Korea is escalating its nuclear threats on South Korea. In the interview, Yoon said he finds it difficult to assure his people of a security guarantee with the current levels of U.S. security commitment.

?“This is an unnecessary dispute. Neither side was talking inaccurately,” said Park Won Gon, a professor at Seoul's Ewha Womans University.?

“The extended deterrence is a commitment and a promise but not a treaty or a binding one,” Park said. “For South Korea, they trust the U.S. but think there should ways to institutionalize it because North Korea's nuclear threats are rising. To do so, (the joint) planning and execution are the key.”

South Korea has no nuclear weapons and is under the protection of a U.S. “nuclear umbrella,” which guarantees a devastating American response in the event of an attack on its ally. But some experts question the effectiveness of such a security commitment, saying the decision to use U.S. nuclear weapons lies with the U.S. president.?

Last year, North Korea test-launched more than 70 ballistic and other missiles capable of reaching the U.S. mainland and U.S. allies South Korea and Japan. In September, North Korea also adopted a new law authorizing the preemptive use of its bombs in a broad range of cases, including non-war scenarios.?

During a recently ended ruling party meeting, North Korean leader Kim Jong Un ordered the “exponential” expansion of his country's nuclear arsenal and the mass-production of tactical nuclear weapons missioned with attacking South Korea, as well as the development of a new ICBM tasked with having a “quick nuclear counterstrike” capability — a weapon he needs to strike the mainland.

Yoon's office didn't provide many details about his government's discussion with the United States. Some observers say South Korea is seeking to obtain a greater role in the U.S. decision-making process on the deployment of its nuclear assets in times of tensions with North Korea.

Kim Taewoo, a former head of Seoul's Korea Institute for National Unification, said the reported South Korea-U.S. discussion likely “benchmarked a NATO-style nuclear-sharing arrangement” that allows NATO member states' warplanes to carry U.S. nuclear weapons. He said the discussion still appears to be falling short of the NATO arrangement because possible nuclear exercises between the two countries would likely be South Korean air force aircraft escorting U.S. aircraft simulating nuclear strikes during joint drills.

“North Korea would take this sensitively. (South Korea and the U.S.) are discussing this to get North Korea to take this sensitively … because that can be a deterrence against North Korea,” Kim Taewoo said.