Russia is believed to have transported tens of thousands of North Korean soldiers to the front lines by rail and air.

North Korea ratified a major defence pact with Russia on Tuesday, outlining mutual military aid and requiring both countries to provide each other with immediate military assistance if attacked.

SEOUL, South Korea — North Korea ratified a major defense treaty with Russia stipulating mutual military aid, the North’s state media reported Tuesday, as the U.S., South Korea and Ukraine say North Korea has sent thousands of troops to Russia to support its war against Ukraine.