According to the Japanese national broadcaster NHK, North Korea may have conducted another nuclear test on Wednesday. A tremor was recorded in North Korea this morning and the Japanese government are checking on the possibility that it was another nuclear test
Some ways the international community can detect nuclear tests, and reasons why it's hard to determine how strong a blast is and whether it is nuclear:
The U.S. Geological Survey Web site recorded a light 4.2-magnitude earthquake in North Korea at 10:35 a.m., about 385 kilometres northeast of the North Korean capital, Pyongyang. Russian equipment in the area had confirmed an underground test and Russian Defence Minister Sergei Ivanov said that the force of the blast was five to 15 kilotons.
"The field of scientific research in the DPRK successfully conducted an underground nuclear test under secure conditions on October 9, 2006, at a stirring time when all the people of the country are making a great leap forward in the building of a great, prosperous, powerful socialist nation. It has been confirmed that there was no such danger as radioactive emission in the course of the nuclear test as it was carried out under scientific consideration and careful calculation. The nuclear test was conducted with indigenous wisdom and technology 100 percent. It marks a historic event as it greatly encouraged and pleased the KPA and people that have wished to have powerful self-reliant defence capability. It will contribute to defending the peace and stability on the Korean Peninsula and in the area around it."
Press release by the official Korean Central News Agency
A seismic wave had been detected at 10:36 a.m. in Hwaderi province near Kilju city on the northeast coast of the PRK Democratic People's Republic of Korea
UGS Data Magnitude: 4.2 (Light) Date-Time: Monday, October 9, 2006 at 01:35:27 (UTC) Location: 41.311°N, 129.114°E Depth: 0 km (~0 mile) set by location program Region: NORTH KOREA Distances: 70 km (45 miles) N of Kimchaek, North Korea