(Seoul) Russian President Vladimir Putin arrived in North Korea early Wednesday for a one-off visit to strengthen defense ties between the two nuclear-armed countries amid Russia’s military operation in Ukraine.

According to a document released by the Kremlin on Tuesday, Russia plans to sign a “strategic partnership” treaty with North Korea. Moscow and Pyongyang have been allies since the end of the Korean War (1950-1953), but have become closer since the Russian assault on Ukraine began in 2022.

During the night, shortly after the presidential plane landed at Pyongyang airport, North Korean leader Kim Jong-un appeared on Russian television greeting Vladimir Putin on a red carpet. Mr. Putin then left the scene in a convoy, passing through streets decorated with Russian flags.

“Russia supported [North Korea] and its heroic people in their struggle to defend their right to choose the path of independence, originality and development for themselves in the confrontation with the cunning enemy , dangerous and aggressive […] and it will unwaveringly support them in the future,” Mr. Putin wrote in an article published by the official North Korean daily Rodong Sinmun and the KCNA agency.

Americans and Europeans have been worried for months about the accelerated rapprochement between Moscow and Pyongyang, accusing the North Koreans of delivering munitions to Russia for its assault on Ukraine in exchange for technological, diplomatic and food assistance.

The trip to North Korea comes nine months after Mr. Putin hosted Kim Jong-un in the Russian Far East, a visit during which the two men praised each other but concluded , officially at least, okay.

Western sources say Pyongyang has been drawing on its vast stockpiles of munitions to massively resupply Russia, and the Pentagon last week accused Moscow of using North Korean ballistic missiles in Ukraine.

In exchange, according to Washington and Seoul, Russia provided North Korea with expertise for its satellite program and sent aid to deal with the country’s food shortages.

In March, Russia used its veto at the UN Security Council to end monitoring of international sanctions violations targeting North Korea, a major gift to Pyongyang.

“What concerns us is the deepening of the relationship between these two countries, not only because of the impact it will have on the Ukrainian people […], but also because there could be some reciprocity that could affect the security of the Korean Peninsula,” said White House National Security Council spokesman John Kirby.

Ukrainian Foreign Minister Dmytro Kuleba urged the international community to counter the “virile friendship” between Vladimir Putin and Kim Jong-un by increasing arms deliveries to Kyiv.

South Korea said Thursday it was “closely monitoring preparations” for Vladimir Putin’s visit.

Seoul has provided significant military aid to Ukraine, where South Korean President Yoon Suk Yeol visited last month, and is taking part in Western sanctions against Moscow.

A few hours before Mr. Putin’s arrival in Pyongyang, “several dozen North Korean soldiers crossed the military demarcation line”, according to the South Korean general staff, before retreating under warning fire from South.  

According to the same source, this incursion – the second in less than two weeks – was accidental.

This is only the second visit to North Korea by the Russian leader, who last visited nearly a quarter of a century ago, shortly after he came to power, to meet with the father of Kim Jong-un, Kim Jong-il.