A passenger walks past a television report on North Korea's nuclear test at a railway station in Seoul - Reuters
A South Korean broacast of its northern neighbour's third nuclear test (Reuters)

North Korea has rebutted criticisms about a third nuclear missile test it has carried out and warned of "further, stronger actions" if the US does not pull back from "belligerent tactics".

Pyongyang claimed the test was an act of self-defence in response to US hostility.

"This nuclear test was only the first response we took - with maximum restraint," an unnamed spokesman for the ministry said in a statement carried by the official KCNA news agency.

"If the United States continues to come out with hostility and complicates the situation, we will be forced to take stronger, second and third responses in consecutive steps."

The test has sparked worldwide condemnation, led by the US president Barack Obama who called it highly provocative. In Britain, Foreign Secretary William Hague said the test "poses a threat to international and regional security". UN chief Ban Ki-moon said he was "gravely concerned" about the negative impact it could have on the region.

However, an expert in North Korea has stated that the test was a "victory" for Kim Jong-un.

"He is likely to be seen as being firmly in command now, at least when considering the international community," Virginie Grzelczyk at Nottingham Trent University said. "This is also likely to strengthen his internal political standing as well, in case there were some who doubted it."

The timing of the test was not random, according to the academic. "This news comes a day ahead of President Obama's State of the Union address," she said.

Although the UN Security Council was expected to condemn the tests, "there are doubts among the international research community that more sanctions could lead North Korea on a different path", added Grzelcyk.

"The current sanctions are creating a cycle of tit-for-tat that is not helpful in resolving the matter. Light nuclear weapons are being developed, and could potentially be launchable in the near future, since North Korea has been working on its delivery and satellite systems as well," she said.

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