A Japanese television broadcaster said North Korea has completed preparations for another nuclear test.

Japan’s Fuji Television cited a Japanese government official as saying all external preparations were seen to be completed for North Korea to conduct a third nuclear test, and that it would not be unusual for Pyongyang to conduct such a test at any time.

The broadcaster said the move prompted Japan and the U.S. to step up alert for possible nuclear detonation by the North.

Earlier this month, a South Korean intelligence source said an additional shaft had been discovered aside from the two tunnels dug for previous nuclear tests the North conducted in Punggye-ri, and that construction there was observed to be coming to an end.

North Korea has already conducted two nuclear tests, one in October 2006 and the other in May 2009.