Beijing on Tuesday dismissed the UN effort, which details crimes including extermination, enslavement, and torture, as 'unreasonable criticism.'
North Korea backed off its threat to block reunions of families split by the Korean War, after Secretary of State Kerry refused to budge on planned military exercises with South Korea.
North Korea is home to one of the world's largest rare earth mineral deposits, but its policy of isolation has long deterred foreign investment.
Until he executed his powerful uncle last month, Kim 'could call up Dennis Rodman but he couldn't call up military strikes,' says one observer. Now concern is rising about the secretive leader.
The reports from South Korea's intelligence services could not yet be independently verified. But they have kicked off a debate about Kim Jong-un's grip on power.
North Korea went on high alert and said the US should forgo planned military exercises with Japan and South Korea. But it could have a hidden agenda.
Defense Secretary Hagel's comments about the North's chemical arsenal come amid new concerns over the sophistication of North Korea's nuclear weapons program.
When North Korea shut down the industrial park it jointly maintained with South Korea in April, it ratcheted tensions to a new high.