CLARK FREEPORT, Philippines—Japan’s defense minister said the threat posed by North Korea has grown to an “unprecedented, critical and imminent level,” reflecting a rising sense of urgency over Pyongyang’s nuclear weapons program.

Japanese Defense Minister Itsunori Onodera told counterparts from South Korea and the U.S. at a gathering of defense ministers of the Association of Southeast Asian Nations here that Japan supports the American position that “all options are on the table”--referring to a possible military response—while...