He told a UN-sponsored conference on disarmament in Geneva that North Korea's measures were "an exercise of restraint and justified self-defence".
"The unity of the Security Council is absolutely crucial", said UN Secretary General Antonio Guterres on Tuesday, while urging countries "to come together with a single strategy to deal with the government of the DPRK".
Talking to news persons in NY, he warned that the solution must be political as confrontational rhetoric may lead to unintended consequences.
The regime of Kim Jong-un claims to have detonated a H-bomb that could be placed in a ballistic missile. "The solution must be political", Guterres said, adding, "The potential consequences of military action are too horrific".
"Nuclear powers understand their responsibilities".
South Korea and the United States are technically still at war with North Korea after the 1950-53 Korean conflict ended with a truce, not a peace treaty.
"We have kicked the can down the road long enough", she added.
North Korea is under mounting global pressure over its missile and military nuclear programs and has been subjected to an array of sanctions by the United Nations.
"I am proud of saying that just two days ago on the third of September, DPRK successfully carried out a hydrogen bomb test for intercontinental ballistic rocket under its plan for building a strategic nuclear force", Han said at the meeting, held in Switzerland, referring to North Korea by its official title, Democratic People's Republic of Korea (DPRK). "But being a nuclear power is not about using those bad weapons to threaten others". He ruled out the possibility of any talks on North Korea's denuclearization, saying Pyongyang's nuclear deterrent is a topic that's off-limits and non-negotiable, in any future dialogue.
He also said it was "ridiculous" that the United States first slapped Russian Federation with sanctions carried in the same bill that penalised North Korea, and "then asked us to help impose sanctions on North Korea".