North Korea said Wednesday it conducted a “successful” hydrogen bomb test.

The announcement on state television came less than a month after North Korean leader Kim Jon Un claimed his country had developed a hydrogen bomb.  The United States and others quickly discounted that claim.

A hydrogen bomb, also known as a thermonuclear bomb, is far more powerful than a atomic bomb.

North Korea conducted three previous nuclear tests in 2006, 2009 and 2013.  All of them took place at the Punggye-ri site, the same area where several monitoring agencies detected man-made earthquake activity on Wednesday morning.

The test prompted emergency national security meetings in South Korea and Japan.

Japanese Prime Minister Shinzo Abe condemned North Korea’s test, calling it a serious threat to Japan’s national security.
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