The defense chiefs of South Korea and the United States have condemned the deployment of North Korean troops to Russia in the “strongest” terms with “one voice.”

Defense Minister Kim Yong-hyun and U.S. Secretary of Defense Lloyd Austin issued the condemnation on Wednesday in a joint statement after the annual Security Consultative Meeting at the Pentagon.

The defense chiefs expressed concern that the military cooperation between North Korea and Russia, which has intensified since the two nations signed a bilateral Comprehensive Strategic Partnership Treaty, is deepening regional instability.

The two sides said military cooperation between Moscow and Pyongyang, including illegal arms trading and advanced technology transfers, constitutes a clear violation of UN Security Council resolutions.

The defense chiefs condemned “in the strongest terms with one voice” the expansion of that military cooperation beyond transfers of military supplies to the actual deployment of forces, and they pledged to closely coordinate with the international community regarding this issue.

The two sides decided that future combined exercises should include appropriate and realistic scenarios, including responses to the use of nuclear weapons by North Korea.