Tanaiste Eamon Gilmore has condemned the test by North Korea of a nuclear device.
The foreign affairs minister warned the action threatens peace and stability on the Korean peninsula and will isolate the country further.
"It is also a major challenge to our efforts to advance global nuclear disarmament and non-proliferation, a long-standing priority of Irish foreign policy," Mr Gilmore said.
"Nuclear weapons are never a means to guarantee peace and security; far from it, they pose the greatest threat of all. The regime in Pyongyang must realise that today's act is reckless and provocative and will only isolate it further from the international community."
North Korea said it had tested a "miniaturised" nuclear device, defying the United Nations' orders to stop building atomic weapons.
Official state media said the test was conducted in a safe manner and aimed at coping with "outrageous" US hostility that "violently" undermined the North's peaceful, sovereign rights to launch satellites.
Mr Gilmore said North Korea must cease all nuclear testing and re-engage with the talks on the denuclearisation of the Korean peninsula, immediately and without pre-conditions.
"Today's events highlight the urgency for the immediate entry into force of the comprehensive nuclear test ban treaty (CTBT)," the Tanaiste added.
"I call on the eight remaining states whose ratification of the treaty is required to do so without delay. While the CTBT has not yet entered into force, it represents an overwhelming international consensus against nuclear weapons testing that Ireland and others have a duty to protect.
"I expect all nations - including North Korea - to respect this international consensus."