SEOUL, South Korea (AP) — North Korea announced Tuesday that its top diplomat is visiting Russia, another sign of deepening ties as South Korea and rival Western nations say the North has sent thousands of troops to 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 left for Russia on Monday, but did not specify the purpose of the visit.

The announcement of Choe’s visit came hours after the Pentagon said North Korea had sent approximately 10,000 soldiers to Russia, which is expected to reach the battlefields of Ukraine in the “coming weeks”.

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

Pentagon spokeswoman Sabrina Singh told reporters on Monday that some of the North Korean soldiers have already moved closer to Ukraine and are believed to be heading toward the Kursk border region, where Russia has been struggling to repel a Ukrainian incursion.

South Korean President Yoon Suk Yeol, in phone calls with European Union Commission President Ursula von der Leyen and NATO Secretary General Mark Rutte on Monday, shared South Korean intelligence assessments that North Korean troops could be deployed to the battlefronts “faster than anticipated”. He called for closer coordination with European governments aimed at “monitoring and blocking” illegal exchanges between Pyongyang and Moscow, Yoon’s office said in a statement.

After initially denying claims of North Korean troop deployments, Pyongyang and Moscow have taken a more vague stance, saying their military cooperation complies with international law, without directly admitting the presence of North Korean forces in Russia.

North Korea has also been accused of supplying Russia with millions of artillery shells and other military equipment to fuel the war in Ukraine. The United States and its partners have described Russia’s purchase of North Korean personnel and supplies as a violation of UN Security Council resolutions and have raised suspicions that Moscow is helping Pyongyang evade sanctions and illegally fund its weapons program.

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

Yoon last week raised the possibility of supplying Ukraine with weapons while he said Seoul was preparing countermeasures that could be implemented in stages, depending on the degree of military cooperation between Pyongyang and Moscow.

South Korea, a growing arms exporter, has provided humanitarian and other non-lethal support to Ukraine and joined US-led economic sanctions against Moscow. It has so far resisted calls from Kiev and NATO to directly supply weapons to Ukraine, citing a long-standing policy of not supplying weapons to countries engaged in active conflict.