Japan plans to dispatch military aircraft to take samples of air to detect radiation in the wake of North Korea's nuclear test on Tuesday, officials and news reports said.
Defence Minister Itsunori Onodera called a meeting of senior defence officials and ordered them to prepare to collect radioactive matter in the air, a ministry spokesman said.
"We are ready to dispatch our aircraft to collect air samples as soon as we receive a request from the prime minister's office," said a spokesman for the Air Self-Defence Force.
Local media said the air force would dispatch trainer aircraft from three air bases in northern, central and southwestern Japan, later in the day.
North Korea confirmed it had "successfully" carried out an underground nuclear test, drawing immediate condemnation from South Korea, Japan and UN leader Ban Ki-moon.