Abe, addressing the UN General Assembly, said that calculations about North Korea needed to change after its latest actions including the state's test of what it said was a miniaturized nuclear bomb for a warhead.
"There is no alternative but to say that the threat has now reached a dimension altogether different from what has transpired until now," Abe said.
"The threat to the international community has become increasingly grave and all the more realistic. It demands a new means of addressing it, altogether different from what we applied until yesterday," he said.
The right-leaning leader first rose to power with tough talk on North Korea and has made revision of Japan's US-imposed pacifist constitution his signature issue.
But Japan has never fired a shot in anger since World War II and is constitutionally barred from offensive military operations.
China and the United States are in talks on drafting a new UN Security Council resolution to punish North Korea for its latest moves, although such measures have not stopped Pyongyang in the past.
China has been increasingly critical of North Korea but many analysts believe that a rising Beijing would prefer to put up with the troublesome regime rather than risk a united, US-allied Korea on its border.
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