Monday's explosion – the latest in a series of hard-line moves by Pyongyang – may have been 20 times more powerful than its last test in 2006.
Presidential Blue House/AP
The test ratchets up tensions between North Korea and the international community, and is the latest in a series of hard-line moves by Pyongyang.
In April it test-launched a long-range missile capable of reaching the United States. It is still holding two US journalists it accuses of spying. It has also kicked out UN inspectors and withdrawn from six-nation talks on its nuclear program.
It's not the first time North Korea has tested a nuclear device – it last did so in 2006.
But Reuters reported that Monday's underground test was a far more powerful explosion than that one. (Click here for a map of the suspected test location, from the Los Angeles Times, and a graphic on how such a test is conducted, from BBC.)
"[North Korea] successfully conducted one more underground nuclear test on May 25 as part of the measures to bolster up its nuclear deterrent for self-defense in every way," its [North Korea's] official KCNA news agency said.
The country's first test in October 2006 was considered to have been relatively weak, about 1 kilotonne, suggesting design problems. Russia's military said the latest test had a force of about 20 kilotonnes.
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