A Chinese paramilitary guard stands on duty outside the North Korean embassy in Beijing on Feb. 12. North Korea's apparent nuclear test had an explosive yield of between six and seven kilotons, South Korea's defense ministry said, revising its earlier estimate of 10 kilotons or more. Ministry spokesman Kim Min-Seok said seismic monitors had detected a tremor with a 4.9 magnitude emanating from the North's nuclear test site.