"We believe new sanctions are indispensable," French Ambassador Francois Delattre told reporters yesterday as he headed into an emergency meeting of the council called to discuss a response to Pyongyang.
"France calls for the adoption as soon as possible of a new resolution under chapter 7" of the UN charter, which provides for sanctions, he added.
The council was meeting at the request of Japan, South Korea and the United States to try to agree on the next steps, but it remained unclear if China, Pyongyang's ally, would support tough measures.
North Korea's state media said the test, which came after a series of ballistic missile launches, had realised the country's goal of being able to fit a miniaturised warhead on a rocket.
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The blast at the Punggye-ri nuclear site had a yield of 10 kilotons, the most powerful to date, according to experts.
The council has strongly condemned North Korea's missile launches and vowed earlier this week to take "further significant measures" against Pyongyang.
Japan and several other council members are calling for new sanctions, but China has repeatedly stressed the need to avoid an escalation of tension on the Korean peninsula.
North Korea has been hit by five sets of UN sanctions since it first tested a nuclear device in 2006.
The council in March adopted the toughest sanctions resolution to date targeting North Korea's trade in minerals and tightening banking restrictions.
Since that resolution, North Korea has carried out 21 ballistic missile launches, Power said, describing those and Pyongyang's second nuclear test this year as "more than brazen defiance.