REPUBLIKA.CO.ID, TOKYO -- The United States may launch unilateral sanctions against North Korea, a U.S special envoy for the isolated state said on Sunday, two days after it carried out its fifth and biggest nuclear test in defiance of U.N. sanctions.

"In addition to action in the Security Council, both the U.S, and Japan, together with the Republic of Korea, will be looking at unilateral measures, as well as bilateral measures, as well as possible trilateral cooperation," said Sung Kim, the envoy, referring to South Korea by its official name.

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.