President Yoon Suk Yeol speaks during an event held in Gangneung, Gangwon Province, Oct. 17. Yonhap

President Yoon Suk Yeol on Friday convened an emergency security meeting amid revelations of North Korea's apparent decision to send troops to Russia to support its war in Ukraine, the presidential office said.

The meeting involving senior officials from the National Security Council, the Ministry of National Defense and the National Intelligence Service (NIS) took place to discuss the latest developments regarding North Korean troops' participation in Russia's conflict with Ukraine.

Following the meeting, the NIS said it believes Pyongyang has recently decided to deploy four brigades, totaling 12,000 soldiers, including special forces, to the war in Ukraine, which would mark North Korea's first large-scale deployment of ground forces.

"The participants agreed that the current situation, in which the military ties between Russia and North Korea have developed from the transfer of military supplies to actual troop deployments, poses a significant security threat not only to South Korea but also to the international community," the presidential office said in a release.

"They also decided not to stand by and will respond by mobilizing all available means in cooperation with the international community," it added.

South Korea has been closely tracking North Korea's troop movement to Russia from the beginning in coordination with its allies, and will continue to monitor the situation and take all necessary measures proactively, according to the office.

On Thursday, Ukrainian President Volodymyr Zelenskyy cited Ukrainian intelligence reports indicating that North Korean personnel have already been deployed in Russian-occupied Ukrainian territories, with an additional 10,000 troops being prepared to join the fight.

Earlier this month, Ukrainian media reported that six North Koreans were among those killed after a Ukrainian missile strike in the partially occupied eastern Donetsk region on Oct. 3. Russia denied using North Korean troops for its war. (Yonhap)