SEOUL, South Korea — A seismic tremor was detected near an underground nuclear test site in North Korea on Sunday, prompting a scramble to determine if the North had conducted a sixth nuclear test in a direct challenge to President Trump.
If the North has tested another nuclear device, it would be an extraordinary show of defiance by North Korea’s leader, Kim Jong-un, against Mr. Trump, who has warned he would unleash “fire and fury” against North Korea if Pyongyang continued to threaten the United States with nuclear missiles.
South Korea’s Defense Ministry and Meteorological Administration said an “artificial” tremor with a magnitude of 5.6, detected at 12:36 p.m. local time, had emanated from the Punggye-ri underground nuclear test in northwestern North Korea. President Moon Jae-in of South Korea called an emergency meeting of his National Security Council in response to the report.
Prime Minister Shinzo Abe of Japan said it appeared likely that the North had carried out its sixth nuclear test. “If North Korea has conducted a nuclear test, we can never accept that,” he told reporters, saying he would call a meeting of his own National Security Council.
Earlier in the day, Mr. Abe and Mr. Trump had spoken by telephone and resolved to put more pressure on North Korea.
Analysts and officials have been warning that North Korea would conduct more nuclear and long-range missile tests, to master the technologies needed to build a nuclear warhead small and sophisticated enough to be fitted onto an intercontinental ballistic missile. Last week, South Korea’s National Intelligence Service told lawmakers in Seoul that North Korea was technically ready to conduct another nuclear test any time at Punggye-ri, where all its previous tests had taken place.
Hours before the tremor was detected on Sunday, North Korea’s state news agency said the country had developed a hydrogen bomb that could be mounted on an intercontinental ballistic missile. The report offered no evidence for the claim, other than photos of Kim Jong-un, the country’s leader, inspecting what it said was the weapon.