Questions remain over whether nuclear-armed Pyongyang has successfully miniaturised its weapons, and whether it has a working H-bomb, but KCNA said that leader Kim Jong-Un had inspected such a device at the Nuclear Weapons Institute.
It was a "thermonuclear weapon with super explosive power made by our own efforts and technology", KCNA cited Kim him as saying, and "all components of the H-bomb were 100 per cent domestically made".
Pictures showed Kim in black suit examining a metal casing with two bulges.
After its fourth nuclear test, in January 2016, it claimed that the device was a miniaturised H-bomb, which has the potential to be far more powerful than other nuclear devices.
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But scientists said the six-kiloton yield achieved then was far too low for a thermonuclear device.
When it carried out its fifth test, in September 2016, it did not say it was a hydrogen bomb.
The North had "further upgraded its technical performance at a higher ultra-modern level on the basis of precious successes made in the first H-bomb test", KCNA said, adding that Kim "set forth tasks to be fulfilled in the research into nukes".
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