North Korean leader Kim Jong Un criticized trilateral military cooperation among the United States, Japan and South Korea for raising tensions in the region and vowed countermeasures, including the further development of nuclear forces.

Kim said U.S. deployments of nuclear strategic assets, war exercises and military cooperation with Japan and South Korea were inviting military imbalance in the region and raising a grave challenge to the security environment, the North's official Korean Central News Agency reported Sunday.

"The DPRK does not want unnecessary tension of the regional situation but will take sustained countermeasures to ensure the regional military balance," Kim said during a visit to the Defense Ministry on Saturday to commemorate the founding day of its army.