The trilateral Freedom Edge exercise comes after North Korea launched a nuclear-capable missile and sent troops to Russia.

The United States is concerned by Russia's growing relationship with North Korea and by what technology the two countries may be exchanging, the top U.S. arms control official said on Wednesday.

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.

Former North Korean soldiers, operating under the name of the Defectors' Propaganda Corps, have delivered materials to Ukraine aimed at encouraging North Korean military personnel serving in the Russian army to desert.