The government slammed North Korea on Wednesday after it apparently conducted another nuclear test, its fourth, which involved what Pyongyang described as a powerful hydrogen bomb.

Prime Minister Shinzo Abe denounced the action as ¡°a grave threat to the safety of our country.¡±

There were stern responses from Seoul and Washington, and China, North Korea¡¯s sole major ally, said it ¡°firmly¡± opposes the blast.