With ballistic missiles flying nearby regularly, Japan and South Korea need little reminder of the threat posed by North Korea and its nuclear arsenal to their neighbors. But the stunning resurrection of a Cold War-era mutual defense pact during Russian President Vladimir Putin’s visit this week to the North Korean capital, Pyongyang, has added to the pressure on some of the Hermit Kingdom’s closest neighbors.

According to the agreement announced by North Korea’s official KCNA news agency on ThursdaycontentPutin and North Korean leader Kim Jong-un agreed that if one side were to fall into a state of war, the other would “provide military and other assistance to the best of its ability without delay.”

Analysts are still teasing out the agreement, trying to figure out how far it might extend to either Mr. Putin’s war in Ukraine or future conflicts on the Korean Peninsula. But the pledge, and signs that Russia might help North Korea continue its quest for a nuclear capability, unsettle officials in Tokyo and Seoul.

Kim Jong-un has become increasingly hostile toward South Korea, abandoning this year his long-standing goal of reunification with the South, even though that goal had seemed unlikely. He now sees South Korea as an enemy to be conquered by nuclear war if necessary, and he frequently tests ballistic missiles toward Japan in a defiant gesture toward the country’s former colonizer.

Analysts say Kim’s alliance with Putin could escalate tensions in Northeast Asia by exacerbating divisions between democratic partners in the United States, South Korea and Japan and the authoritarian camps of Russia, North Korea and China.

“This is bad news for international efforts to stop North Korea’s nuclear and missile development,” said Koh Yu-hwan, former president of the Seoul-based Korea Institute for National Unification.

Putin’s protracted war in Ukraine has prompted him to deepen his relationship with Kim Jong Un. U.S. and South Korean officials say he sought and received Soviet-style munitions from Pyongyang. Both Moscow and Pyongyang deny the accusation.

The war in Ukraine has had a major impact on the region. “Today’s Ukraine could be tomorrow’s East Asia,” Japanese Prime Minister Fumio Kishida often says.

“President Putin has not ruled out the possibility of military-technical cooperation with North Korea, and we express serious concern about this,” Yoshimasa Hayashi, chief cabinet secretary to Kishida, told a news conference in Tokyo.

South Korea strongly criticized the deal, calling it “sophisticated and absurd” for North Korea and Russia – which have a history of waging war on the Korean Peninsula and Ukraine, respectively – to pledge military cooperation under the assumption that they would be attacked first.

“We emphasize that any cooperation that directly or indirectly helps North Korea strengthen its military is a violation of UN Security Council resolutions and should be monitored and sanctioned by the international community,” the South Korean government said in a statement. It also vowed to strengthen defense cooperation with the United States and Japan to counter nuclear and missile threats from North Korea.

Separately, President Yoon Seok-yeol’s national security chief, Jang Ho-jin, said South Korea would “reconsider” its policy of not providing Ukraine with lethal weapons for use in a war with Russia.

In some ways, the meeting between two authoritarian leaders desperate for outside support felt predictable to the United States and its Asian allies, who have been preparing for growing security challenges from North Korea and China in recent years, sometimes facing domestic political resistance.

Japan vows to increase defense budget andExpanding operations within the limits of the peace constitutionAfter years of frosty relations, Kishida and Yoon agreed to strengthen bilateral ties between the two countries and establish a closer trilateral partnership with the United States toEstablishing mutual security arrangementsThe three countries have participated in more than 60 trilateral diplomatic meetings, military exercises and intelligence sharing over the past year, according to the U.S. Embassy in Tokyo.

“I think it shows that President Biden, President Kishida and President Yoon were very prescient in using their political capital,” Rahm Emanuel, the U.S. ambassador to Japan, said in an interview. “Not only was it very prescient from a political perspective, but it was also very prescient from a strategic perspective because now Russia and North Korea” may be developing weapons together.

At this fraught global moment, the revival of North Korea and Russia’s Cold War-era commitment to mutual defense has alarmed other countries in the region.

“I think what’s more dangerous is that this suggests that the relationship may be longer lasting than we initially thought and may be more strategic rather than transactional,” said Bruce Klingner, a senior fellow for Asian studies at the Heritage Foundation in Washington. “We don’t know how far the two countries will go in supporting each other.”

At the very least, it shows that Russia is willing to flagrantly ignore UN sanctions.

“It wasn’t that long ago that Russia supported U.N. sanctions against North Korea,” said James Brown, a political science professor at Temple University’s Tokyo campus who specializes in Russia’s relations with East Asia. “So this confirms that not only is Russia not enforcing sanctions, it’s actively undermining them and will help North Korea evade them.”

In Seoul, the meeting between Putin and Kim is likely to reopen discussions about whether South Korea should consider arming itself with nuclear weapons and fuel speculation about what might happen if Trump is re-elected as U.S. president.

“South Korea should now fundamentally review its current security policy because it relies almost entirely on the U.S. nuclear umbrella to deal with North Korea’s nuclear threat,” said Chung Sang-chang, director of the Korean Peninsula Strategy Center at the Sejong Institute.

In some ways, growing ties between Russia and North Korea could help underpin Tokyo and Seoul’s recently restored ties, and their trilateral cooperation with the U.S. Many analysts worry that a change of government in the U.S. or South Korea could jeopardize such ties. (Japan is seen as relatively stable.)

“In a way, it provides a rationale for continuing trilateralism after Trump comes to power, or if progressives come to power in South Korea,” said Jeffrey Hornung, a senior political analyst specializing in Japan at the RAND Corporation in Washington. “While it doesn’t change what Seoul or Tokyo should do, it certainly adds a new factor that they have to consider.”

But an editorial in Seoul’s left-leaning daily Hankyoreh questioned the wisdom of close cooperation between the United States, Japan and South Korea, saying it has put South Korea “on a collision course with China and Russia, which have a huge influence on the political situation on the Korean peninsula. It is time to reflect on whether this biased diplomatic approach has led to the development of North Korea-Russia relations.”

Despite the drama in Pyongyang this week, some analysts say the biggest concern in the region remains China’s growing military ambitions.

“Maritime construction in the East China Sea or the South China Sea, space, cyber and multi-domain warfare capabilities all justify our new policy,” said Kunihiko Miyake, a former Japanese diplomat and special adviser to the Canon Institute for Global Studies in Tokyo. He said Putin’s visit to North Korea was “just another example of an existential threat in Asia, not the biggest one.”