North Korea's nuclear weapons test carried out early Monday was relatively small, US media claimed amid additional reports that Washington had been informed by China of the impending test shortly before it was carried out.
The power of the blast was equivalent to around 550 tonnes of TNT explosive, reports said quoting a South Korean state geological body.
The US-detonated atom bomb which destroyed the Japanese city of Hiroshima during the Second World War in comparison was equivalent to around 21,500 tonnes of TNT.
US news channel Fox News quoted security analysts as saying that from Pyongyang's point of view the test could be viewed as a disappointment. Experts described the explosion as "more of a sizzle than a bang."
White House spokesman Tony Snow meanwhile said it would take some time to gauge how accurate North Korea's claims regarding the test were.
US President George W Bush had been informed of North Korea's plans to test a nuclear weapon shortly before the event, US media additionally reported citing White House sources.
Reports said Pyongyang informed China of the impending test an hour before it was conducted. The government in Beijing contacted the US embassy in the Chinese capital, who then immediately informed US Secretary of State Condoleezza Rice of the development.
The US president was then briefed on the situation at around 10 pm Sunday evening (0730 am IST, Monday) by security advisor Stephen Hadley.
The White House condemned the test as a "provocative act" and called on the UN Security Council "to act immediately" to North Korea's unprovoked action.
DPA
