Whatever the explosive yield, the device was undoubtedly powerful, and the test offers the first hint that North Korea could be more developed in its nuclear program than previously thought.
The country has for years worked on nuclear miniaturization, which means creating a nuclear warhead small and light enough to be fired over long distances.
In a high-level national security meeting, South Korean President Moon Jae-in called the test "an absurd strategic mistake" that will lead to the international community further isolating Pyongyang.
But the sanctions that have been implemented to isolate the country have in many ways failed. The Kim regime has developed its weapons and nuclear program despite the measures that have crippled the economy and exacerbated periods of mass starvation.
The White House will be under global pressure to deliver a coherent response to North Korea.
It has been accused of sending mixed messages on the issue and lacking a clear strategy.
Trump's administration is now pursuing what it calls a strategy of "peaceful pressure" to get North Korea to bring its nuclear weapons program to the negotiating table.
China is also under pressure to do more to deter North Korea's provocations as its most powerful ally and patron. Beijing condemned the test Sunday.
"We strongly urge (the) North Korea side to face up to the firm will of the international community on the denuclearization of the peninsula, abide by relevant resolutions of the UN Security Council, stop taking wrong actions that exacerbate the situation and are not in its own interest, and return to the track of resolving the issue through dialogue," the Chinese Foreign Ministry said in a statement.
