First Vice Foreign Minister Kim Hong-kyun, right, speaks to Russian Ambassador to South Korea Georgy Zinoviev at the Government Complex Seoul after summoning him regarding North Korea's deployment of troops to support Russia's fight against Ukraine. Courtesy of Ministry of Foreign Affairs

South Korea strongly urged Russia on Monday to take "immediate" action to withdraw North Korean troops from the war in Ukraine, after Seoul's spy agency confirmed the North's deployment of its soldiers to Russia to help the war effort.

First Vice Foreign Minister Kim Hong-kyun called in Russian Ambassador to Seoul Georgy Zinoviev to deliver the government's "grave stance" and "strongly call for the immediate withdrawal of North Korean troops and stop relevant cooperation" with Pyongyang, the foreign ministry said in a release.

Kim pointed out that their military cooperation going beyond military supply provisions poses a serious threat to South Korea and the international community, while amounting to violations of multiple U.N. Security Council resolutions.

Kim "condemned in the strongest terms the illegal military cooperation, including the North's troop deployment, and sternly warned that South Korea will respond with every possible means, with the international community, to any acts that threaten the core interests of South Korea," the ministry said.

Zinoviev told Kim that the cooperation with North Korea is "not directed against South Korea's security interests," the Russian Embassy in Seoul said in a Facebook post later.

The ambassador emphasized that the cooperation is "carried out within the framework of international law," and noted that Russia and South Korea have "opposing positions about the reasons behind the growing tensions on the Korean Peninsula," the posting read.

South Korea's National Intelligence Service (NIS) said last week that the North sent 1,500 soldiers to Russia's Far East earlier this month to fight in Russia's war in Ukraine and is preparing to send more troops.

The NIS said the North Korean soldiers have been supplied with Russian military fatigues and weapons. They are training at a base in Vladivostok and other sites to be deployed to battlefields, the agency said.

The NIS released satellite images and other photos showing what it says are Russian navy ships moving near a North Korean port to transport North Korean soldiers.

The North's deployment, if true, would mark a significant development in its relationship with Moscow since they forged closer ties with a new treaty committing them to mutual military support in case either is attacked.

The deployment would suggest that the North is getting Russia's help in advanced military technologies for its weapons programs in return, as widely suspected by the United States and its allies.

Washington has not confirmed the reports about the North Korean troop deployment to Russia, saying there is no evidence and that they are evaluating the situation. (Yonhap)