North Korean troops have begun engaging in combat operations alongside Russian forces, the U.S. State Department said on Tuesday, expressing concern that Russia had turned to North Korea for soldiers to fight in its war with Ukraine.

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.

North Korea ratified a defense treaty with Russia, state media reported Tuesday, formally deepening military cooperation that has seen Pyongyang send thousands of troops to help Moscow in 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.

North Korea has ratified a mutual defence treaty with Russia signed by the two countries' leaders in June, which calls for each side to come to the other's aid in case of an armed attack, state media KCNA said on Tuesday.

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. Russia had already completed its side of the ratification last week after the pact was signed by Russian President Vladimir Putin and North Korean leader Kim Jong Un.