North Korea says it carried out a test of what it described as a hydrogen bomb designed for a long-range missile.
US President Donald Trump was convening his national security team on Sunday to weigh options including drastic economic sanctions against North Korea after Pyongyang detonated what it claimed was a hydrogen bomb able to fit atop a missile.
The US president said in a tweet that the time for "appeasement" was over, and a top adviser said Trump was weighing "all our options."
"The national security team is monitoring this closely," said White House press secretary Sarah Huckabee Sanders, in announcing the urgent meeting on a US holiday weekend.
In a Twitter message, Trump denounced the unexpectedly powerful test -- said to be the North's first blast to exceed in magnitude the atomic bombing of Hiroshima, Japan -- as "very hostile and dangerous to the United States."
North Korea said its test of what it described as a hydrogen bomb designed for a long-range missile was "a perfect success."
The United Nations Security Council will meet at 10 am (1400 GMT) on Monday to discuss the issue at the request of the United States, Japan, Britain, France and South Korea, the US mission to the UN said in a statement on Sunday.
TRT World’s Sara Firth reports.
The Sunday blast was so powerful that US monitors measured a 6.3-magnitude earthquake near the North's main testing site, and it was felt in China and Russia.
Pyongyang residents threw their arms aloft in triumph as a jubilant television newsreader hailed the "unprecedentedly large" blast; she said it had moved the country closer to "the final goal of completing the state nuclear force."
Condemnation from world capitals was swift, including from China and Russia while South Korean President Moon Jae-In called for the "strongest punishment."
Trump, who has waged an on-again-off-again war of words with the North's leader Kim Jong-Un, refrained from direct threats on Sunday.
But in a Twitter message he branded the North "a rogue nation which has become a great threat and embarrassment to China, which is trying to help but with little success."
Trump has repeatedly insisted that Beijing lean heavily on its isolated neighbour to halt its nuclear and missile development.
On Sunday, however, the US president also aimed criticism at the government in Seoul. South Korea, Trump said, "is finding, as I have told them, that their talk of appeasement with North Korea will not work, they only understand one thing!"
TRT World's Tetiana Anderson has the latest from Washington.
'Cut off North Korea'
A series of US and United Nations-backed sanctions against the North have had little apparent effect on Pyongyang, as Kim has repeatedly seemed to brush off Trump's strongest warnings.
But US Treasury Secretary Steven Mnuchin said on Sunday that his department was preparing potent new measures that would completely "cut off North Korea economically."
"I'm going to draft a sanctions package and send it to the president for his strong consideration that anybody that wants to do trade or business with them will be prevented from doing trade or business with us," Mnuchin said on "Fox News Sunday."
But he also said Trump had made it clear that he will "look at all our options."
While the United States has virtually no trade with the North, the burden of sanctions such as Mnuchin described would fall heavily on China, which buys about 90 percent of North Korean exports.
Hours before the test, the North released images of Kim at his country's Nuclear Weapons Institute, inspecting what it said was a miniaturised H-bomb that could be fitted onto an intercontinental ballistic missile (ICBM).
China, the North's sole major ally, issued a "strong condemnation" of the test.
Chinese President Xi Jinping and Russian President Vladimir Putin agreed to "appropriately deal with" North Korea after the test, state news agency Xinhua said."
The two leaders agreed to stick to the goal of denuclearisation on the Korean Peninsula and keep close communication and coordination to deal with the new situation," Xinhua said in a brief dispatch.
TRT World spoke to Sandy Huang from Xiamen, China for the latest.
Japanese Prime Minister Shinzo Abe described the test as "absolutely unacceptable" while Russia's foreign ministry expressed "strongest condemnation" but urged calm.
In Seoul, President Moon Jae-In called for new United Nations sanctions to "completely isolate North Korea."
He said the South would discuss deploying "the strongest strategic assets of the US military" -- a possible reference to tactical nuclear weapons, which the US withdrew from South Korea in 1991.
Tremor felt in China, Russia
While US Secretary of State Rex Tillerson spoke by phone with his Asian counterparts, US and South Korean military chiefs also conferred.
Seoul's defence ministry said the respective chairmen of the joint chiefs of staff -- General Jeong Kyeong-Doo and General Joseph Dunford -- had "agreed to prepare a South Korea-US military counteraction and to put it into action at the earliest date."
US monitors measured a 6.3-magnitude tremor near the North's main testing site, which South Korean experts said was five to six times stronger than that from a 10-kiloton test a year ago.
The quake was felt in northeastern China, with people in the border city of Yanji saying they fled their homes in their underwear, and in the Russian Pacific city of Vladivostok.
Chinese monitors said a second tremor of 4.6 magnitude could be due to rock over the underground blast site giving way.Pyongyang raised tensions in July with two successful tests of an ICBM which apparently brought much of the US mainland within range.
Last week it fired a missile over Japan.
Trump has warned Pyongyang that it faces "fire and fury" and that Washington's weapons are "locked and loaded."
But even some Trump advisers say US military options are limited when Pyongyang has the capacity to quickly wipe out much of the South Korean capital Seoul.
'Super explosive power'
Analysts believe Pyongyang's weapons program is aimed both at self-defence and strengthening its hand in any negotiations with the US.
"North Korea will continue with their nuclear weapons program unless the US proposes talks," Koo Kab-Woo of Seoul's University of North Korean Studies said.
Pictures of Kim at the Nuclear Weapons Institute showed the young leader examining a metal casing shaped like a peanut shell.
The device was a "thermonuclear weapon with super explosive power" entirely made "by our own efforts and technology," the Korean Central News Agency cited Kim as saying.
Analysts cautioned that the image had not been verified. But the blast clearly was -- it was detected as far away as Germany.