The United States today sternly admonished North Korea against acts that could "further destabilize" the region, amid claims that it successfully tested a new engine designed for an inter-continental ballistic missile that could reach US shores.
"We have seen the reports of North Korea's claims to have developed new engine technology for its ICBMs," read a statement from State Department Deputy Spokesman Mark Toner.
"We call on North Korea to refrain from actions and rhetoric that further destabilize the region and focus instead on taking concrete steps toward fulfilling its commitments and international obligations," Toner said.
North Korea said its breakthrough would "guarantee" an eventual nuclear strike on the US mainland.
It was the latest in a series of claims by Pyongyang of significant new inroads in both its nuclear weapons and ballistic missile programs, although outside experts have treated a number of the claims with skepticism.
According to the North's official KCNA news agency, the ground engine test was ordered and personally monitored by the hermit nation's enigmatic leader Kim Jong-Un.
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In a statement, the US Geological Survey said a magnitude 5.3 earthquake was detected near North Korea's nuclear test site.
According to CNN, the US Air Force is expected to start flying its "radiation sniffer" jet off the Korean Peninsula in the coming hours to take air samples to see if it can determine a nuclear event occurred in North Korea.
"The Air Force WC-135 jet, dubbed the "Constant Phoenix," will look for distinctive elements a nuclear test of any type would emit into the air. The collected samples can be analysed to determine exactly what occurred," it said.
"Our monitoring stations picked up an unusual seismic event in the Democratic People's Republic of Korea (DPRK) today at 00:30 (UTC). So far, 25 of our stations are contributing to the analysis," CTBT Organisation's executive secretary Lassina Zerbo said in a statement.
"The event seems to have been slightly larger than the one our system recorded on 6 January this year and the location is very similar to that event. Our initial location estimate shows that the event took place in the area of the DPRK's nuclear test site.
"If confirmed as a nuclear test, this act constitutes yet another breach of the universally accepted norm against nuclear testing; a norm that has been respected by 183 countries since 1996," she said.
