WASHINGTON—Close cooperation with Japan and South Korea will continue to be vital for the United States as the world faces growing security challenges from Russia and North Korea, a senior Biden administration official said.

In an exclusive interview days before Donald Trump returns to the White House, Mira Rapp-Hooper, senior director for East Asia and Oceania at the National Security Council, said the trilateral partnership “must continue no matter who is in office.”

“We have increased the benefits of our three countries continuing to cooperate and reduce the risk that any one of us will see fit to disrupt that cooperation in the future,” Mira Rapp-Hooper, also a special assistant to U.S. President Joe Biden, told The Asahi Shimbun on Jan. 7.

The United States believes that North Korea has provided millions of rounds of ammunition, short-range ballistic missiles and other weapons and also dispatched more than 10,000 soldiers to Russia, which continues its aggression against Ukraine.

As concerns grow that North Korea might gain military technology in return, Pyongyang’s increasing cooperation with Moscow is adversely impacting the security environment from Europe to Asia.

“We are greatly concerned about DPRK-Russia cooperation,” Rapp-Hooper said, referring to North Korea by the acronym of its official name, the Democratic People’s Republic of Korea.

“This is going to be a challenge that is with us for some time to come. I expect the new U.S. administration will have to devote significant attention to it as well.”

Rapp-Hooper, who has played a central role in the White House’s Indo-Pacific policy, indicated that the Biden administration has struggled to deal with North Korea, acknowledging that Pyongyang has never shown willingness to meet with U.S. officials.

Still, she underscored the importance of seeking dialogue with North Korea to respond to the threats the country poses.

“We continue to see value in the DPRK engaging with the United States or with either one of our allies, whether that’s Japan or the ROK,” she said, referring to South Korea using the acronym for the Republic of Korea.

The Biden administration has focused on collaboration with Japan and South Korea partly to counterbalance the military cooperation between Russia and North Korea.

But some observers say the future of the three-way cooperation has been threatened by Trump’s return to power and the political turmoil in South Korea following President Yoon Suk-yeol’s short-lived declaration of martial law in December.

Rapp-Hooper said the United States has long tried to ensure that the trilateral partnership will be “institutionalized” for the long term.

She said the partnership has expanded to include not only national security aspects, such as conducting joint training and sharing real-time data on North Korean missile launches, but also economic security and assistance to Southeast Asia and Pacific island nations.

She added that the relationships have been cemented with the three countries now working together across government agencies and at all levels of government.

Asked about the continuing crisis in South Korea, Rapp-Hooper said, “Obviously, it is no secret that this is a time of deep uncertainty for the ROK, but we do believe in the ROK’s democratic resilience.”

She said Washington responded to the martial law declaration “with great concern” and communicated to Seoul the importance of domestic stability and procedures in accordance with its Constitution.

Asked about China’s increasing assertiveness in the region, Rapp-Hooper said Beijing has “increased its pressure” on its neighbors in recent years, citing the Taiwan Strait and surrounding waters as well as the Second Thomas Shoal in the South China Sea as examples.

She said Japan has been “second to none as a partner to the United States in seeking to address those concerns.”

Rapp-Hooper noted that Tokyo decided to increase defense spending to 2 percent of gross domestic product under the previous Kishida administration and also began talks with Washington on joint production of defense equipment, such as the Patriot surface-to-air missile.

“We see a Japan that is increasingly equipping itself to contribute to Indo-Pacific peace, stability and security for the long term,” she said.

Rapp-Hooper emphasized the significance of expanding U.S.-Japan joint military exercises in and around Japan’s southwestern Nansei Islands. Such exercises are considered to be aimed at preparing for a possible Taiwan contingency.

She described them as part of efforts to “to send credible signals of deterrence to demonstrate to any potential challenger that the U.S.-Japan alliance is modern, it’s operational, it’s synchronized and it’s prepared for any type of threat that it may face in the years ahead.”

Washington and Tokyo have been bolstering coordination between the command and control functions for the U.S. military and the Self-Defense Forces.

Rapp-Hooper said the work is “well under way” and will “properly equip this alliance to respond operationally to threats in the region wherever they may come from.”

The Biden administration has also strengthened cooperation among the United States, Japan and the Philippines to keep China in check.

“I hope and expect that that is a partnership that you will see continue in the next administration as well,” Rapp-Hooper said.