North Korea said Tuesday its top diplomat is visiting Russia, in another sign of their deepening relations as rival South Korea and Western nations say the North has sent thousands of troops to support Russia’s war in Ukraine.

North Korea’s official Korean Central News Agency said a delegation led by Foreign Minister Choe Son Hui departed for Russia on Monday, but didn’t specify the purpose of the visit. In a closed-door hearing at South Korea’s parliament, the South’s spy agency said Choe may be involved in high-level discussions on sending additional troops to Russia and negotiating what the North would get in return, according to Lee Seong-kweun, a lawmaker who attended the meeting.

The announcement of Choe’s visit came hours after the Pentagon said North Korea has sent to Russia about 10,000 troops, who are likely to fight against Ukraine within “the next several weeks.”

Concern in West

South Korean and Western leaders have expressed concern that North Korean involvement could help prolong Russia’s aggression in Ukraine, and that Russia may offer technology in return that could advance the threat posed by North Korea’s nuclear weapons and missile program.

Maj. Gen. Pat Ryder, the Pentagon press secretary, said a “relatively small number” of North Korean troops are now in the Kursk region, where Russia has struggled to push back a Ukrainian incursion. He declined to provide a more precise number. A couple thousand more troops are heading in that direction, he told reporters Tuesday.

“As of right now, you know, it remains to be seen exactly how the Russians and the North Koreans will employ these forces,” Ryder said, adding that he expects the deployment to be discussed by Defense Secretary Lloyd Austin, Secretary of State Antony Blinken and their South Korean counterparts when they meet in Washington this week.

Cooperation seen

South Korea’s National Intelligence Service told lawmakers it’s examining the possibility that some groups of North Korea’s military personnel in Russia, including generals or other high-ranking officials, may have already moved to frontline areas. The spy agency said the two sides appear to be struggling to resolve communication issues, although the Russian military is training North Korean troops on Russian military terminology, Lee said.

The agency said space-based reconnaissance is an area where North Korea is likely receiving Russian help. It said North Korea may be acquiring advanced components from Russia as it prepares to launch another military reconnaissance satellite following a failed attempt in May, said Park Sun-won, another lawmaker who attended the hearing.

North Korea first placed a spy satellite in orbit last November. Its leader Kim Jong Un has described those assets as crucial for monitoring South Korean and U.S. military activities and enhancing the threat of his nuclear-capable missiles.

Threat to Seoul

In a telephone conversation with Ukrainian President Volodymyr Zelenskyy, South Korean President Yoon Suk Yeol said deepening military cooperation between North Korea and Russia could pose a “major security threat” to Seoul if the North gains access to Russian technology and its troops get combat experience.

The leaders confirmed plans to exchange government delegations as part of efforts to strengthen communication and coordinate their responses over the conflict, Yoon’s office said.

In earlier calls with European Union Commission President Ursula von der Leyen and NATO Secretary-General Mark Rutte, Yoon called for closer coordination with European governments aimed at “monitoring and blocking illegal exchanges” between Pyongyang and Moscow.

Behind the scenes

After initially denying the claims about North Korean troop deployments, Pyongyang and Moscow have adopted a vaguer stance, asserting that their military cooperation conforms with international law without directly admitting the presence of North Korean forces in Russia.

North Korea has also been accused of providing millions of artillery shells and other military equipment to Russia to fuel its war in Ukraine. The United States and its partners have described Russia’s procurement of North Korean personnel and supplies as a violation of U.N. Security Council resolutions, and raised suspicions that Moscow is helping Pyongyang to evade sanctions and unlawfully finance its weapons program.

Russia, along with China, has blocked U.S.-led efforts at the Security Council to tighten sanctions on North Korea over its recent missile testing, which intensified after Russia’s invasion of Ukraine in 2022. Russia also vetoed a U.N. resolution to extend the mandate of monitors in March, in a move that effectively abolished oversight by U.N. experts of Security Council sanctions against North Korea. It prompted Western accusations that Moscow was acting to shield its arms purchases from Pyongyang.

“The illegal military collusion between Russia and North Korea poses a significant security threat to the international community and a serious matter that could potentially harm our security. We must thoroughly examine all possibilities and prepare countermeasures,” Yoon said in a Cabinet meeting in Seoul on Tuesday.

Yoon last week raised the possibility of supplying Ukraine with weapons while saying Seoul is preparing countermeasures that could be rolled out in stages depending on the degree of military cooperation between Pyongyang and Moscow.

South Korea, a growing arms exporter, has provided humanitarian aid and other non-lethal support to Ukraine and joined U.S.-led economic sanctions against Moscow. It has so far resisted calls by Kyiv and NATO to directly supply Ukraine with weapons, citing a longstanding policy of not providing arms to countries engaged in active conflict.