The test could have brought North Korea closer to developing a nuclear warhead capable of striking the west coast of the US.

Pyongyang officials admitted that a "miniaturised" nuclear device had been set off, with a greater explosive force than those used in two previous nuclear tests, in 2006 and 2009 reports The Guardian.

"It was confirmed that the nuclear test that was carried out at a high level in a safe and perfect manner using a miniaturised and lighter nuclear device with greater explosive force than previously did not pose any negative impact on the surrounding ecological environment," KCNA, the North's official news agency, announced.

However, seismic activity was detected by a number of monitoring bodies,  as the quake registered at magnitudes between 4.7 and 5.2.

Yosuke Igarashi, an official at the Japan Meteorological Agency, said: "A natural earthquake normally starts with a smaller tremor followed by a larger one. This quake's strength was the same throughout."

Barack Obama said the test was a highly provocative act that violated security council resolutions and posed a threat to US and international security.

The US president called for "further swift and credible action by the international community" against North Korea.

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