North Korea carried out its most powerful nuclear test yet on Sunday, claiming it detonated a hydrogen bomb designed to be loaded onto an intercontinental ballistic missile. North Korean state television described the nuclear test as a “perfect success.”
Analysts have expressed skepticism about the claims of an H-bomb ― a device far more powerful than the atomic bombs that devastated Hiroshima and Nagasaki in 1945 ― but the international community expressed “grave concern” at the apparent advancement in North Korea’s nuclear capabilities.
According to the U.S. Geological Survey, the nuclear test caused a shallow magnitude 6.3 earthquake. A South Korean official told The New York Times this meant the explosion was at least “five to six times” more powerful than North Korea’s previous nuclear test, which took place last September.
In a series of tweets posted a few hours after the detonation, U.S. President Donald Trump called North Korea a “rogue nation” that continues “to be very hostile and dangerous to the United States.
Trump, who previously threatened North Korea with “fire and fury,” went on to say that South Korea’s “talk of appeasement” is not working. “They only understand one thing” he said, without elaborating.
“We’ll see,” Trump said later on Sunday when a reporter asked the president as he was returning from church if he planned to attack North Korea.
Trump convened a meeting of national security officials at the White House and afterward Defense Secretary warned that any attack on the U.S. or its allies would be met by “a massive military response.” He said the response would be “both effective and overwhelming.”
“We have many military options” he told reporters outside the White House, and Trump was briefed on them.
North Korean leader Kim Jong Un “should take heed of the United Nations Security Council’s unified voice,” Mattis said. “All members unanimously agreed on the threat North Korea poses, and they remain unanimous in their commitment to the denuclearization of the Korean Peninsula, because we are not looking to the total annihilation of a country, namely North Korea. But as I said, we have many options to do so.”
Nikki Haley, the U.S. ambassador to the U.N., said on Twitter that she had called for an emergency meeting of the security council on Monday morning.
Trump also tweeted on Sunday that he was considering “stopping all trade with any country doing business with North Korea.”
U.S. Treasury Secretary Steve Mnuchin told Fox News on Sunday that he would put together new sanctions against Pyongyang aimed at cutting off all trade.
North Korea’s nuclear test comes amid uncertainty surrounding the free trade deal between South Korea and the U.S., which Trump has criticized.
Trump said on Saturday that he would be mulling over the fate of the U.S-Korea Free Trade Agreement in the coming days. Axios reported that the president was “seriously considering withdrawing” from the deal.
In the immediate aftermath of Sunday’s nuclear test, Washington conducted emergency calls with allies Japan and South Korea.
U.S. National Security Adviser H.R. McMaster spoke with his South Korean counterpart, Chung Eui-yong, for 20 minutes about an hour after the blast, according to the Associated Press.
Seoul has called for the “strongest possible” response from the international community, including new sanctions to “completely isolate” its northern neighbor, the BBC reported.
China’s Ministry of Foreign Affairs said in a statement that it “resolutely opposes” the nuclear test, while the Russian foreign ministry said North Korea’s blatant disregard of international law deserved “the strongest condemnation.”
German Chancellor Angela Merkel and French President Emmanuel Macron said they intend to tighten European Union sanctions on North Korea, and British Prime Minister Theresa May said the UN Security Council should consider new measures, Reuters reported.
Yukiya Amano, head of the U.N. nuclear watchdog, called North Korea’s nuclear program “a matter of grave concern.”
“This new test, which follows the two tests last year and is the sixth [by North Korea] since 2006, is in complete disregard of the repeated demands of the international community,” said Amano, director general of the International Atomic Energy Agency.
The test occurred mere hours after North Korean media reported Pyongyang had developed a hydrogen bomb that could be carried by an intercontinental ballistic missile ― a munition system that could possibly reach the U.S. mainland. Images had been circulated of Kim inspecting an hourglass-shaped warhead.
Though analysts said Sunday that they doubt North Korea has truly developed a hydrogen bomb, experts said the country’s nuclear capabilities were evidently improving.
Kim Dong-yub, a defense analyst in Seoul, told The New York Times he believed the test on Sunday involved a “boosted” atomic bomb. Nuclear weapons expert David Albright told the paper the power of the device suggested it contained “thermonuclear material.”
Vipin Narang, a Massachusetts Institute of Technology professor who specializes in nuclear strategy, described the weapon tested as a “city buster.”
“Now, with even relatively inaccurate intercontinental ballistic missile technology, [North Korea] can destroy the better part of a city with this yield,” Narang told The Washington Post.
Sunday’s test is the latest in a series of recent provocations by North Korea. It fired a missile over Japan in late August, causing the Japanese government to urge citizens in the missile’s path to take shelter. Tokyo harshly condemned that launch, the first time since 2009 that a North Korean projectile has taken a path over Japan.
That incident also prompted Trump, as he had done before, to suggest an American military response as a possible option.
North Korea and the U.S. have long been in an intractable diplomatic standoff, but the relationship has deteriorated this year as Pyongyang’s nuclear and missile programs rapidly advance.
The situation intensified in early August, after the Post reported that North Korea had successfully miniaturized a nuclear warhead, a key step toward being able to fire a nuclear weapon that could reach the U.S. mainland.
Since then, Trump and North Korea have exchanged heated rhetoric, and the U.N. has moved to put stricter sanctions on Pyongyang. Trump made his “fire and fury” threat in early August and tweeted that “talking is not the answer!” Other White House officials, including Mattis, subsequently tried to walk back his statements.
North Korea has reacted to Trump’s remarks and the international condemnation directed at it by repeatedly threatening the U.S. island territory of Guam. In response, Mattis has said that any missile headed toward the island would be shot down.
The U.S. and its allies have several missile defense systems in place around the region, and the U.S. military has been testing its missile defenses in response to North Korea’s increasingly brazen launches.
On Aug. 30, U.S. military officials announced they had successfully shot down a intermediate-range ballistic missile during a test at a base in Hawaii ― the same type of missile that North Korea had fired over Japan days earlier.
This article has been updated with comments from U.S. Defense Secretary Jim Mattis.