TOKYO North Korea's conducted a nuclear test on Friday and, combined with advances made by the Pyongyang regime in mobile ballistic missile technology, posed a grave threat to Japan, Defence Minister Tomomi Inada said.
"We can't deny the possibility that North Korea is miniaturising a device to build a warhead," Inada said at a press briefing in Tokyo.
She also said the magnitude of the tremor suggested it was not a test of a hydrogen device.
(This version of the story corrects genders in paragraph 3)
(Reporting by Nobuhiro Okubo; writing by Tim Kelly; Editing by Raju Gopalakrishnan)