South Korean scientists say they have detected a radioactive gas from North Korea's most recent nuclear test, adding that they cannot be certain whether the test had been for a hydrogen bomb.
Pyongyang conducted its sixth nuclear test earlier this month, prompting the UN Security Council to step up sanctions against the country.
North Korea has denounced the sanctions, but US President Donald Trump say they do not go far enough.
More, Seoul released a new video, showing their preparation for a possible attack on Pyongyang.
Al Jazeera's Andrew Thomas reports from Seoul.
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