CCTV9英语新闻：朝鲜已进行了三次核试验（在线收听）

Since 2006, the DPRK has conducted three nuclear tests at the Punggye-ri nuclear test site, the latest was in February 2013. 

On October 9th, 2006 the DPRK announced it has successfully conducted an underground nuclear test. The country said it was facing the US extreme threat of a nuclear war. Many observers thought the test was in political need, as the leaders of the DPRK and South Korean were holding talks and the South Korean Pan Ki-moon was named as UN Secretary-General. Some analysts also believed the DPRK wanted to push the US back to negotiations and lift economic sanctions on the country. 

And analysis said the DPRK's another underground nuclear test on May 25th, 2009 is to bring its people together to push forward the domestic reform. On February 12th, the DPRK conducted the third nuclear test, after the UN approved the No. 2087 resolution. Pyongyang said the test was an act of self-defense against "US hostility".