Speaking in the South Korean capital Seoul, Kerry said the recent test of a new submarine-launched ballistic missile (SLBM) showed that North Korea had no genuine interest in engaging with the international community.
"Instead, it continues to pursue nuclear weapons and ballistic missiles, it continues to break promises and make threats, and it continues to show flagrant disregard for international laws," he told a joint press conference with South Korean Foreign Minister Yun Byong-Se.
The impoverished but nuclear-armed state is already heavily sanctioned following a series of nuclear and missile tests staged in violation of UN resolutions.
Just over a week ago, the North said it had successfully test-fired an SLBM, defying a UN ban on its use or testing of ballistic missile technology.
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A fully-developed SLBM capability would take the North Korean nuclear threat to a new level, allowing deployment far beyond the Korean peninsula and the potential to retaliate in the event of a nuclear attack.
He specifically cited "stories of grotesque, grisly, horrendous public displays of executions" carried out on a personal whim by Kim -- often against those closest to him.
South Korea's intelligence agency reported last week that North Korea's defence minister, Hyon Yong-Chol, had been purged and most likely executed for insubordination and dozing off during a formal military rally.
The agency said it had unverified reports that the execution had been carried out at close range with a high-calibre anti-aircraft gun.