North Korea's participation in Russia's aggression against Ukraine, which gives its troops the opportunity to gain practical combat experience, signals that the war is starting to affect the security situation in East Asia, making the Japanese government wary of the possibility of Pyongyang beefing up its military capabilities.

"The military cooperation between North Korea and Russia, including the dispatch of North Korean troops in the war, is expected to cause the situation in Ukraine to deteriorate even further, and we should be seriously concerned over the matter in light of the impact on the security environment surrounding our country," Chief Cabinet Secretary Yoshimasa Hayashi told a news conference Friday.

At a meeting in Pyongyang in June last year, Russian President Vladimir Putin and North Korean leader Kim Jong Un signed a comprehensive strategic partnership agreement calling for mutual support in the event of an emergency.