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 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.

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 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.

"Today I can confirm that over 10,000 (North Korean) soldiers have been sent to eastern Russia, and most of them have moved to the far western Kursk Oblast, where they have begun engaging in combat operations with Russian forces,

North Korea troops have begun fighting alongside Russians, a U.S. State Department spokesman said during a briefing on Tuesday. "Over 10,000 DPRK (North Korean) soldiers have been sent to eastern Russia,