In the contest of global narratives, China has sought to cast itself as a peaceful nation opposed to dividing the world into rival camps. In contrast, it has accused the United States of building alliances that will drive the world toward a new Cold War.

Yet Russia and North Korea’s mutual defense treaty, which calls for the two countries to provide immediate military assistance to each other in the event of war, is exactly the kind of bloc-building that China has charged the United States with. China’s closest strategic partner and its only treaty ally — Russia and North Korea — are now the ones heightening the risk of Cold War-style confrontation in northeast Asia.

The pact also creates more headaches for Beijing by appearing to deepen the semblance of a trilateral axis between China, Russia and North Korea, which China has sought to avoid. “Beijing has very carefully stayed away from the optics of a China-Russia-North Korea axis,” said Yun Sun, the director of the China program at the Stimson Center in Washington. “It wants to keep its options open.”

Japan, South Korea and the United States could now decide that the threat posed by a Russian and North Korean defense treaty requires them to enhance their own security arrangement, announced last year at Camp David, by increasing troop levels or strengthening defenses along China’s periphery.

For those reasons, China’s top leader, Xi Jinping, might not welcome the budding bromance between President Vladimir V. Putin of Russia and Kim Jong-un, the leader of North Korea. Meeting in Pyongyang on Wednesday, Mr. Putin and Mr. Kim heralded the defense agreement as the beginning of a new era in their relations.

The pact also exposed the limitations of China’s partnerships with both countries, analysts said.

Mr. Xi has declared a “no limits” relationship with Mr. Putin and pledged “unswerving” support for North Korea — linking arms with two like-minded authoritarian countries to push back against what they regard as American bullying around the world.

But by aligning with two pariah states, Mr. Xi is also at risk of facing fallout from the actions of their unpredictable leaders. Mr. Putin’s invasion of Ukraine has severely damaged China’s relationship with the West, which has accused Beijing of not doing enough to rein in Russia. And Mr. Kim’s nuclear saber rattling has helped bring two tense neighbors — Japan and South Korea — together in a trilateral defense partnership with the United States.

Fears already abound that Russia may provide North Korea with technology to bolster Pyongyang’s nuclear weapons program in exchange for munitions for use in Ukraine.

Mr. Xi can ill afford more surprises at a time when he needs to turn around China’s struggling economy. Despite his increasingly adversarial tone toward the West, Mr. Xi remains invested in maintaining China’s position in the current economic global order.

“The new pact between Putin and Kim is not good news for Beijing,” said John Delury, a professor of Chinese studies at Yonsei University in Seoul. “Xi Jinping has never had an easy relationship with the headstrong Korean dynast and now has increasing reason to worry about Putin encouraging Kim’s aggressive tendencies.”

Between the war in Ukraine and the risk of conflict on the Korean Peninsula, Mr. Delury said, “Putin and Kim are forces of instability at a time when China benefits from an orderly environment.”

China has sought to distance itself from the new pact, with a spokesman at the Foreign Ministry on Thursday declining to comment, saying it was a Russian and North Korean issue.

In reality, the Russia-North Korea treaty, coupled with the alliance between the United States, Japan and South Korea, has “significantly exacerbated” the risk of “confrontation, rivalry or conflict” in the region, in China’s view, said Shi Yinhong, an international relations professor at Renmin University in Beijing.

Mr. Shi said peace on the Korean Peninsula was a top priority for China, and the increasing militarization of the region put one of “China’s vital interests at stake.”

China still holds considerable sway over Russia and North Korea. The United States contends the Kremlin would not be able to sustain its war in Ukraine if China did not buy massive quantities of Russian oil or supply Russia with consumer goods and dual-use technologies, like chips and machine tools, to fuel its war machine. At the same time, North Korea relies on China for virtually all its trade, including food and energy.

That sway over Moscow and Pyongyang has bolstered Beijing’s importance at times when other countries have called on China to use its influence — unsuccessfully — to rein in North Korea’s nuclear buildup or Russia’s war in Ukraine.

But Mr. Putin’s wooing of Mr. Kim creates a new competitor for Beijing for influence over North Korea, creating “a windfall for Kim and a headache for Xi Jinping,” said Danny Russel, a diplomacy and security analyst at the Asia Society Policy Institute.

“Importantly for Pyongyang, the partnership with Putin — while not without limits — generates valuable leverage against Beijing,” Mr. Russel said. “Playing major powers off against each other is a classic play in Korean history, and North Korea’s massive dependence on China in recent decades has been a liability that Kim Jong-un is eager to reduce.”

“The scorecard shows North Korea gaining the most by far, with China potentially the biggest loser,” he added.

Keeping the Kim regime in power is a priority for Beijing to preserve a buffer between the Chinese border and U.S.-led forces stationed in South Korea.

China and North Korea officially say they are as close as “lips and teeth,” but relations between the two neighbors have long been fraught, with a mix of mutual mistrust and common interests.

Since taking power in 2011, Mr. Kim has made China uncomfortable by rapidly increasing the number of missile tests and expanding North Korea’s nuclear weapons program. Mr. Xi initially refused to meet with Mr. Kim. It was only when President Trump announced plans to meet with the North Korean dictator that Mr. Xi changed course, eventually holding talks with Mr. Kim in 2018, before and after the summit with Mr. Trump.

Mr. Xi could now feel compelled again to meet with Mr. Kim, said Victor D. Cha, a professor of government and international affairs at Georgetown University and the Korea chair at the Center for Strategic and International Studies in Washington, because “Xi cannot afford to let Putin flaunt all of this influence over his neighbor.”

The growing closeness of Russia and North Korea could give China more of an incentive to try to repair and stabilize ties with South Korea.

On the same day Mr. Putin and Mr. Kim met in Pyongyang, Chinese diplomats and military officials met with their South Korean counterparts in Seoul. China wants to drive a wedge between Washington and Seoul in hopes of weakening South Korea’s military alignment with the United States.

At the meeting, according to Chinese state media on Wednesday, Beijing said that the Korean Peninsula’s priority should be to cool tensions and avoid moves that would intensify confrontation — language that is vague enough that it could be read as a critique of either the United States or the Russia-North Korea pact. Despite its alliance with the North, Beijing sought to depict itself as a neutral player in the dispute, saying that it has always “determined its position based on the right and wrong of the matter itself.”

Olivia Wang contributed reporting from Hong Kong.