North Korea is claiming to have carried out its controversial threat to conduct its first-ever nuclear weapons threat.
The isolated communist regime says it carried out a successful underground blast this morning in defiance of international warnings not to go ahead.
South Korean and US officials have confirmed that a tremor was felt at the time of the alleged test and that it was not a natural occurrence.
North Korea attracted worldwide condemnation last week when it said it was planning a nuclear test in response to "US hostility".
The matter is expected to be discussed today by the UN Security Council, with the US and Japan likely to push for further sanctions on Pyongyang.