US Defense Secretary Lloyd Austin warned Tuesday that if an adversary challenges South Korea or the United States, it would be challenging the two countries' "alliance as a whole," reaffirming America's "ironclad" security commitment to the Asian ally.

Austin issued the warning in an exclusive contribution piece to Yonhap News Agency, as he plans to hold talks with South Korean Defense Minister Lee Jong-sup in Seoul later in the day to discuss deterrence against evolving North Korean nuclear and missile threats.

"This commitment includes US conventional, nuclear and missile-defense capabilities, as well as the forward presence of 28,500 US uniformed personnel (in Korea)," the secretary said in the piece titled "The Alliance Stands Ready."

He added, "So our adversaries and competitors know that if they challenge one of us, they are challenging the US-ROK alliance as a whole." ROK stands for the South's official name, the Republic of Korea.

His remarks came after North Korean leader Kim Jong-un raised the need for an "exponential" increase in his country's nuclear arsenal and named the South an "undoubted" enemy during a key ruling party gathering held in December.

Touching on the purpose of his visit, Austin sketched out plans to deepen cooperation and discuss the mutual security challenges. "I am also here to reaffirm that the US extended deterrence commitment to the ROK is ironclad," he said.

Austin characterized the Seoul-Washington partnership as "one of the most capable, interoperable and adaptable alliances in history" and highlighted the allies' "determination" to confront the North Korean challenge.

In a show of the alliance's military heft, he referred to a raft of formidable assets, including the fifth-generation F-35 fighter aircraft and the U-2 surveillance aircraft at Osan Air Base.

He called for the allies to "remain vigilant."

"Over the past several decades, the Democratic People's Republic of Korea has developed its nuclear, ballistic-missile and other weapons programs," he said, referring to the North by its official name. He also stressed that the North conducted an unprecedented number of missile launches in defiance of UN Security Council resolutions last year.

To meet the persistent threats, Austin stressed a range of the allies' security efforts, such as expanding the scope and scale of their combined exercises and incorporating "live-fire" elements.

He also stressed the importance of deepening tripartite cooperation with Japan, including conducting trilateral ballistic missile defense and anti-submarine warfare exercises.

"When the United States, the ROK and Japan stand together, we are all safer," he said.

Further, Austin pointed to the US' dispatch to the Korean Peninsula of "some of our most capable platforms," like the F-35 and the F-22 radar-evading aircraft, as a crucial sign of Washington's commitment to its ally.

"The deployment of advanced assets to the ROK on a rotational basis highlights our readiness for any contingency -- and it stands as a clear reminder of America's unwavering commitment to the ROK's security," he said.

To cement deterrence, Austin made clear the allies' commitment to do "even more," including "increasingly complex" scenario-based tabletop exercises focused on nuclear threats on the peninsula and visits to strategic sites housing advanced US capabilities.

Aside from the North Korean issue, the secretary noted the allies are looking ahead beyond their longstanding focus on promoting security on the Korean Peninsula.

"We are also modernizing our alliance to ensure our two countries can continue to contribute to sustaining a free, open and prosperous Indo-Pacific, including further discussions on helping our partners in Southeast Asia build their own capabilities," he said. (Yonhap)