Japan is "deeply concerned" over North Korea's progress in developing intercontinental ballistic missiles, calling the advances emblematic of the "new level of threat" posed by the reclusive state, the Defense Ministry said in its annual white paper unveiled Tuesday.

The report also concluded in more definite terms than last year that Pyongyang has made "significant headway" in its nuclear arms development, citing its "possible" ability to develop miniaturized nuclear warheads that can fit on the tips of its missiles.

The paper also ratcheted up Japan's condemnation of China's continued maritime muscle-flexing, expressing "strong concerns" over its activities in both the East and South China seas.