Lima, Peru — U.S. President Joe Biden met with leaders of South Korea and Japan to discuss a “coordinated” response to the deployment of thousands of North Korean troops to help Moscow’s war against Ukraine and on Pyongyang’s nuclear threat more broadly. Biden met with South Korean President Yoon Suk Yeol and Japanese Prime Minister Shigeru Ishiba Friday, on the sidelines of the Asia-Pacific Economic Cooperation Forum in Lima, Peru. Biden said the countries aim to link arms “to secure the technologies of the future and countering North Korea’s dangerous and destabilizing cooperation with Russia.” Yoon underscored North Korean troops deployment as a reminder of the “challenging security environment within and outside the region.” Pyongyang’s troop deployment is a “significant development” that the U.S. will treat “with the seriousness with which it deserves to be treated,” White House national security adviser Jake Sullivan told reporters aboard Air Force One en route to Lima, Thursday. Sullivan said the leaders will prepare for any potential moves from Pyongyang, including nuclear testing and ballistic missile launches as the U.S. prepares for a change of administration when Donald Trump takes office in January. “Transitions have historically been time periods when the DPRK has taken provocative actions,” Sullivan said, using the abbreviation for North Korea’s formal name, the Democratic People’s Republic of Korea. The leaders highlighted ongoing cooperation on “trilateral interoperability by sharing data in real time about ballistic missile launches” by Pyongyang and strengthening U.S. extended deterrence cooperation with Seoul and Tokyo. Extended deterrence The United States has an “extended deterrence” policy that aims to prevent adversaries from attacking allies, including South Korea and Japan. The policy states that Washington will come to their aid if they are attacked, potentially including use of American nuclear capabilities. No specific announcement on extended deterrence was made Friday. However, the summit is an opportunity to “ensure that each of these two bilateral dialogues are working to reinforce one another, and that there aren’t gaps and seams between them,” Sullivan said. The leaders announced the establishment of a trilateral secretariat as part of their efforts to “institutionalize” three-way cooperation that began as a series of leaders’ dialogues on economic security, intelligence sharing, and defense policy coordination. The trilateral leaders’ dialogues began in May 2023 on the sidelines of the G7 summit in Hiroshima, Japan, and then at Camp David in August that year. The trilateral effort is one of Biden’s signature regional security initiatives to push Seoul and Tokyo to overcome years of animosity and work together to deter common adversaries, North Korea and China. U.S., Japanese and South Korean militaries Thursday launched joint exercises in waters south of the Korean peninsula and west of Japan, the final drills under the Biden administration. During his first term, Trump advocated for friendlier ties with North Korean leader Kim Jong Un but also threatened to attack his country. He pressured Tokyo and Seoul to take on a larger share of U.S. defense burden-sharing. “Both Tokyo and Seoul are worried, what sort of asks he [Trump]’s going to have at them, to maintain the level of alliance that’s in both countries today,” said Darcie Draudt Vejares, fellow for Korean studies at the Carnegie Endowment for International Peace. A day before Trump’s reelection, the U.S. and South Korea finalized a new agreement for Seoul to pay $1.13 billion in 2026 to support U.S. troops, an 8.3% increase from the previous year. A senior administration official briefing reporters after the trilateral said that the leaders did not raise any concerns about the incoming administration. The focus of the conversation was on common challenges and shared interests that are “enduring,” the official said. Bilateral meetings with Peru, China Biden also met separately Friday with summit host, Peruvian President Dina Boluarte. Biden announced a $65 million counternarcotics assistance package for Peru, which includes transferring nine Black Hawk helicopters over the next five years to support Lima’s fight against narcotics trafficking and organized crime. He highlighted other initiatives, including rail and space cooperation. On Saturday, Biden is scheduled to meet with Chinese President Xi Jinping, their last in person engagement while the U.S. president is in office. “It’s an important opportunity to mark the progress that we’ve made in the relationship and also to manage it through this delicate period of transition where we want to maintain a degree of stability, even as we continue to compete vigorously with the PRC [People’s Republic of China],” said Sullivan. Beijing will be looking ahead to the incoming Trump administration that has threatened higher tariffs on Chinese goods, he told VOA. “I doubt Xi Jinping is going to want to preface what he’ll do with Donald Trump,” said Zack Cooper, a senior fellow at the American Enterprise Institute. “I’m not even sure that the probability of tariffs will come up in the meeting.” Biden and Xi are expected to revisit areas of cooperation, particularly the resumption of military-to-military contact, combating the global fentanyl crisis and nascent work to deal with the risks of artificial intelligence (AI), a senior administration official said in a briefing with reporters earlier this week. In Peru, Xi will inaugurate a $1.3 billion megaport, part of China’s infrastructure investment program that has bought him influence in various parts of the world. A senior administration official told reporters that during his meeting with Boluarte, Biden cautioned the Peruvian leader that it’s important for countries to “maintain very high standards of transparency in their dealings with other partners around the world, including China.”