North Korea has ratified a landmark defense pact with Russia, state media reported Tuesday, deepening security cooperation that has seen Pyongyang send thousands of troops to help Moscow fight Ukraine.

The agreement formalizes months of tightening military bonds between two nations that were communist allies throughout the Cold War.

Seoul and ally the United States have accused the nuclear-armed North of sending thousands of soldiers to Russia, where they have been outfitted with Russian uniforms and are, according to reports, massed on the border near Kursk.