US Defense Secretary Lloyd Austin reaffirmed America's "ironclad" deterrence commitment to South Korea and Japan on Tuesday, stressing that Washington remains "clear-eyed" about security challenges from North Korea, China and Russia.

During his talks with Japanese Defense Minister Gen Nakatani in Tokyo, Austin also underscored the United States' commitment to advancing what he called "historic" trilateral cooperation with South Korea in the face of shared threats.

The Pentagon chief's remarks came amid concerns that the aftermath of South Korean President Yoon Suk Yeol's botched martial law attempt could have an impact on security coordination between Seoul and Washington, and that Pyongyang could engage in provocative acts at a time of political uncertainty in Seoul.

"Let me be clear (that) America's extended deterrence commitment to Japan and to the Republic of Korea is ironclad," Austin said, referring to a US pledge to mobilize all of its military capabilities, including nuclear, to defend its allies.

Enumerating a series of security issues, Austin said the US is meeting the challenges with "confidence" and "resolve."

"Now, we're clear-eyed about the challenges to peace and stability in this region and worldwide, and that includes coercive behavior by the People's Republic of China in the East China Sea and the South China Sea, and elsewhere in the region," he said.

"It includes Russia's reckless war of choice in Ukraine, and it includes the DPRK's support for Moscow's war, as well as its other destabilizing and provocative activities," he added. DPRK is short for North Korea's official name, the Democratic People's Republic of Korea.

Portraying the regional security situation as "increasingly severe," Nakatani highlighted the need to continue reinforcing the allies' defense capabilities.

He also pointed out that multilateral cooperation with South Korea, Australia and others has progressed.

Earlier in the day, Austin visited Yokota Air Base in Tokyo, where the US Forces Japan is headquartered, and Yokohama North Dock, a US Army facility in Yokohama, as he seeks to cement the Biden administration's legacy of deepening regional alliances and partnerships.

At the air base, he met with new USFJ commander Lt. Gen. Stephen Jost and discussed ongoing efforts to upgrade USFJ to a joint force headquarters under a project to enhance contingency response capabilities between the US and Japan.

At Yokohama North Dock, he received a briefing on the US Army's security activities in Japan, and met service members from US Army Japan and the Army's 5th Composite Watercraft Company.

The watercraft company was activated in February. It is the first time that an Army Composite Watercraft Company has been deployed outside the US.