US and South Korean officials took part in a simulated "table-top" exercise that focused on the possibility of North Korea using a nuclear weapon, the Pentagon said on Thursday.

Nuclear-armed North Korea launched an unprecedented number of missiles last year, including intercontinental ballistic missiles (ICBMs) capable of reaching the US mainland. On Monday it launched two missiles into the Pacific Ocean.

US and South Korean officials have also warned the North could be preparing for its first test of a nuclear device since 2017.

This was the 8th US and South Korean deterrence strategy committee table-top exercise, known as DSC TTX, and the first edition since they agreed last year to hold the drills annually.

"Given the DPRK's recent aggressive nuclear policy and advancements in nuclear capabilities, the (table-top) scenario focused on the possibility of the DPRK's use of nuclear weapons," a Pentagon statement said, using the acronym of the country's official name, the Democratic People's Republic of Korea.

"The US and South Korea delegations focused their discussion on Alliance deterrence to maintain peace and stability on the Korean Peninsula and potential options for responding to DPRK nuclear weapons use," the statement added but did not say specifically what scenarios were played out.

Seoul's defence ministry said the allies reaffirmed their readiness for any North Korean nuclear threats and agreed to continue reinforcing intelligence sharing, crisis consultation, joint planning and execution of extended deterrence.

"The US side stressed that any use of nuclear weapons by North Korea against the United States or its allies and friends would be unacceptable and result in an end of its regime," the ministry said in a statement.

After the simulated exercise was carried out at the Pentagon on Wednesday, officials from both countries visited Naval Submarine Base Kings Bay in Georgia.

"The delegations discussed how best to leverage (South Korea's) non-nuclear capabilities to support nuclear deterrence against DPRK nuclear threats," the statement added.

Since taking office in May, South Korean President Yoon Suk-yeol has been pushing to bolster confidence in American extended deterrence - its military capability, especially nuclear forces, to deter attacks on its allies - as Pyongyang strives to secure its capacity to strike anywhere in the United States.

In November, Yoon warned of an unprecedented joint response with allies if North Korea goes ahead with a nuclear test.

- Reuters