The UN yesterday set up a commission of inquiry into human-rights violations in North Korea, saying some "may amount to crimes against humanity".
The 47-member Geneva forum unanimously adopted a resolution brought by the European Union and Japan, and backed by the United States, condemning alleged torture, food deprivation and labour camps for political prisoners.
It launched a three-member investigation for a year and called on Pyongyang to co-operate with the team, which will include Marzuki Darusman, its special rapporteur on North Korea who last month reported rapes, torture and executions in the country.
"This long-awaited inquiry will help expose decades of abuse by the North Korean government," Julie de Rivero, advocacy director at Human Rights Watch, said in a statement.
At the debate, North Korean Ambassador So Se-pyong rejected the resolution as "an instrument that serves the political purposes of the hostile forces in their attempt to discredit the image of [North Korea]".
"As we stated time and again, those human-rights abuses mentioned in the resolution do not exist in our country," So said, warning that the sponsors should be held accountable "for all serious consequences".
The UN body's move comes amid heightened tension in the region after North Korea threatened retaliation for UN sanctions imposed for its nuclear test and launch of a long-range rocket in December. Pyongyang blames Seoul and Washington for leading the push to punish the North.
Earlier yesterday, North Korea threatened strikes on US military bases in Japan and Guam, further escalating tensions. The tone of the threat, attributed to a spokesman of the army's supreme command, blended with the torrent of war-like rhetoric churned out by Pyongyang in recent weeks, but stood out for its precise naming of targets.
Military tensions on the Korean Peninsula are at their highest level for years, with Pyongyang irate at the use of nuclear-capable US B-52 bombers and nuclear submarines in ongoing joint military drills with South Korea.
"The US should not forget that the Andersen base on Guam, where B-52s take off, and naval bases on the Japan mainland and Okinawa, where nuclear-powered submarines are launched, are all within the range of our precision target assets," the army spokesman said.
North Korea has successfully tested medium-range missiles that can reach Japan, but has no proven long-range missile capability that would allow it to hit targets on Guam, more than 3,200 kilometres away.
US Defence Secretary Chuck Hagel announced last week that Washington had decided to bolster missile defences along the US west coast to "stay ahead of the threat" from North Korea.
North Korean leader Kim Jong-un had issued a more general threat to destroy US bases "in the operational theatre of the Pacific" on Wednesday, as he directed a drone strike exercise. Still photographs broadcast on state television seemed to show what looked like a rudimentary drone being flown into a mountainside target and exploding.
It is extremely rare for North Korean media to specify the day on which Kim attended a drill. It also said a rocket defence unit had successfully shot down a target that mimicked an "enemy" Tomahawk cruise missile.
Additional reporting by Agence France-Presse