Russian assistance does not appear to have directly strengthened North Korea’s military yet, but the rapid and expanding cooperation between the two countries could boost Pyongyang’s armed forces over the medium to long term, Japan’s Ministry of Defense (MOD) warned in its latest white paper released Tuesday.

The annual report on regional security developments and the activities of the MOD and Self-Defense Forces described North Korea’s military as posing “an even more grave and imminent threat” to Japan’s national security than ever.

The MOD identified deepening Russia-North Korea military cooperation as one of the most significant developments affecting regional security.