South Korea’s National Intelligence Service on Friday disclosed three satellite photos of Russian naval vessels transporting North Korean special forces soldiers.

The agency said that the ships transported roughly 1,500 North Korean troops from a North Korean region to the Russian Far Eastern city of Vladivostok from Oct. 8-13. It also confirmed the North has decided to dispatch around 12,000 troops from special operations brigades to support Russia in its war with Ukraine.

Ukraine's Center for Strategic Communication and Information Security on Saturday released a video via its official X account showing what it claimed were North Korean soldiers lining up and receiving uniforms and equipment at a training ground in Russia's Far East region.

CNN revealed a copy of questionnaires prepared in Russian and Korean asking North Korean soldiers about the sizes of their uniforms and boots.

In the face of mounting evidence that North Korea is sending troops to Russia apparently to fight Ukraine, Pyongyang is keeping silent.

If true, it is the first time North Korea has dispatched ground troops abroad to intervene in an international conflict. The North has previously sent contingents of military advisers, mostly to earn foreign currency, but there is no precedent for a large dispatch of its elite troops to carry out combat missions.

North Korea has become a key supplier of artillery shells and missiles to Russia in the ongoing conflict with Ukraine. Now, Pyongyang has gone farther. This is a grave issue that threatens global security.

If a member of the North Atlantic Treaty Organization goes to war against Russia in response to the North Korean intervention, the nature of the war will change. It is also hard to exclude the possibility that North Korean military support turns the tide of the war. Russia has reportedly experienced a deepening shortage of soldiers on the front lines due to heavy casualties.

Above all, the North’s troop dispatch causes concern because it comes after North Korean leader Kim Jong-un signed a comprehensive strategic partnership agreement with Russian President Vladimir Putin in June in Pyongyang.

Under the treaty, if either Russia or North Korea is attacked and enters a state of war, the other party will provide military and other assistance using all available means. There is a high likelihood that when they signed the agreement, Kim promised to send not only munitions but also troops in return for food, petroleum and above all, Russian technology essential to upgrading the North’s nuclear weapons and missiles.

If the North secures a military surveillance satellite with the help of Russia, it will be able to monitor South Korea and US forces in real time.

If the North perfects an intercontinental ballistic missile capable of striking the American mainland, the US nuclear deterrent may be neutralized.

If the North secures a nuclear-powered submarine, security on the Korean Peninsula will be badly shaken.

In an emergency, Pyongyang will likely demand the same level of cooperation from Russia.

Putin is likely to give Kim what he wants in return for sending troops.

The massive troop dispatch indicates that Russia-North Korea ties are moving beyond the provision of rifles, shells and short-range missiles to the level of a blood alliance.

North Korea’s recent moves are unusual. It exploded all of the northern parts of the roads and railroads to the South. Kim furthermore defined South Korea as an enemy state and is fortifying the North's land border with the South.

Close military cooperation between North Korea and Russia is an urgent threat to South Korean security as well as to the international community.

South Korea, together with its allies, must monitor their military cooperation closely. The South must join forces with rules-based, like-minded democracies and organizations, including the UN and the EU, to increase the pressure on North Korea and Russia. They must be made to pay the price for violating UN sanctions and international laws and threatening global security.