SEOUL: South Korea's presidential Blue House will hold a National Security Council meeting at 0200 GMT on Friday after seismic activity was detected near North Korea's known nuclear test site, activity South Korea said could have been a nuclear test. The South Korean prime minister will preside over the meeting, a Blue House official said by telephone. South Korea's military has convened a crisis management team after the US Geological Survey recorded a seismic event with a magnitude of 5.3 in North Korea, the defence ministry in Seoul said in a statement.