Japanese Prime Minister Shinzo Abe on Wednesday condemned a hydrogen bomb test conducted by North Korea, saying the test was a "significant threat".
Japan has held its national security council meeting immediately after a 5.1-magnitude quake was detected around 10.30 a.m. (local time) in the northeastern part of North Korea, Xinhua reported.
North Korea's official media said the country has successfully conducted its first hydrogen bomb test. Pyongyang had conducted three nuclear tests in 2006, 2009 and 2013.
"The hydrogen bomb test is a significant threat to Japan's national security and is unacceptable," Abe said, adding Japan will consider sanctions against North Korea as its nuclear test violates UN Security Council's relevant resolutions.
Japan lifted part of its own sanctions against North Korea since the two countries reached an agreement that Pyongyang agreed to re-investigate the whereabouts of Japanese nationals it allegedly abducted four decades ago.
Abe also said Japan will work with the US, South Korea, China and Russia to cope with the issue.
Meanwhile, Japanese Foreign Minister Fumio Kishida will hold talks with the US Ambassador Caroline Kennedy over the nuclear test.