Specific details of the U.S. unilateral sanctions have yet to be decided, Kim said, speaking to reporters in Tokyo after meeting Japanese foreign ministry officials.
But both the U.S. and Japan were looking at "a full range of possibilities, in terms of additional unilateral sanctions that can be implemented," he added.
North Korea on Friday set off its most powerful nuclear explosion to date, saying it had mastered the ability to mount a warhead on a ballistic missile, ratcheting up a threat that its rivals and the United Nations have been powerless to contain.
The UN Security Council denounced North Korea`s decision to carry out the test and said it would immediately begin working on a resolution. The U.S., Britain and France pushed for the 15-member body to impose new sanctions.
"We will be working very closely in the Security Council and beyond to come up with the strongest possible measure against North Korea`s latest actions," said Kim.
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