SEOUL, South Korea (AP) — 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.

Russia had completed the ratification of the treaty last week after it was signed by Russian President Vladimir Putin and North Korean leader Kim Jong Un in June. It is considered both countries’ biggest defense deal since the end of the Cold War.