North Korea said Sunday that it successfully tested a miniaturized hydrogen bomb capable of fitting on an intercontinental ballistic missile (ICBM).

State television said the test ordered by leader Kim Jong Un was "perfect success" and a "meaningful" step forward.

South Korea said earlier that Pyongyang appeared to have conducted a nuclear test after an artificial earthquake was detected in northern North Korea, according to the Yonhap News Agency.

Such a move would represent a remarkable show of defiance on the part of Kim against President Trump amid heightened tensions between Washington and Pyongyang.

The artificial quake was detected around 12:30 p.m. local time Sunday in the North Hamgyong Province, the Korea Meteorological Administration reported.

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The U.S. Geological Survey said it recorded a 6.3-magnitude earthquake on Sunday, described as a "possible explosion," near North Korea's known nuclear test site in the northeast.

The office of South Korean President Moon Jae-in said that the North may have conducted its sixth nuclear test, and he called an emergency meeting of his security council, Yonhap reported.

Meanwhile, Japan's foreign minister told members of the media that North Korea had conducted its sixth nuclear test — the first since Trump took office.

Trump threatened last month to unleash "fire and fury" if North Korea continued to threaten the U.S. with nuclear weapons, and the North in recent days conducted four ballistic missile launches.

The presumed nuclear test came after North Korea said earlier in the day Sunday that it had developed a hydrogen bomb capable of being loaded onto an ICBM.

Updated: 7:17 a.m.