US president responds to escalation by Kim Jong-un, calling North Korea ‘a rogue nation which has become a great threat’.

Amid alarm from world leaders over North Korea’s claim that it can now, for the first time, put a nuclear warhead on an intercontinental ballistic missile, Donald Trump upped the ante on Sunday with a series of provocative statements.

Asked outside church in Washington whether plans to attack the isolated, hostile dictatorship, the US president replied: “We’ll see.”

He and the first lady were whisked back to the White House from St John’s Episcopal church in an SUV. Shortly afterwards, Trump tweeted: “I will be meeting General Kelly [John Kelly, chief of staff], General Mattis [James Mattis, defense secretary] and other military leaders at the White House to discuss North Korea. Thank you.”

Earlier in the day, after news emerged overnight that North Korea was believed to have detonated a large hydrogen bomb in a test in the north of the country, deepening the biggest foreign policy challenge faced by his administration, Trump posted a series of tweets.

“North Korea has conducted a major nuclear test,” the president tweeted on Sunday morning. “Their words and actions continue to be very hostile and dangerous to the United States.”

He added: “North Korea is a rogue nation which has become a great threat and embarrassment to China, which is trying to help but with little success.”

And he also accused South Korea of favouring a policy of “appeasement”, telling Seoul that “will not work” because the North Koreans “only understand one thing!”

In a surprise announcement on state TV, North Korea said it had tested a powerful hydrogen bomb that could be loaded on to an intercontinental ballistic missile, in a move that is expected to increase pressure on Trump to defuse the growing nuclear crisis on the Korean peninsula.

Pyongyang said the test, its sixth since 2006, had been a “complete success” and involved a two-stage thermonuclear weapon of unprecedentedstrength.

White House press secretary Sarah Huckabee Sanders issued a statement, saying Trump would meet with his national security team later on Sunday to discuss the North Korean nuclear test.

“The national security team is monitoring this closely,” she wrote. “The president and his national security team will have a meeting to discuss further later today. We will provide updates as necessary.”

There has been no independent verification of North Korea’s claims that it has achieved a key goal in its nuclear programme – the ability to miniaturise a warhead so that it can fit on a long-distance missile.

The regime has earlier released footage of what it said was a hydrogen bomb that would be loaded on to a new ICBM.

The TV announcement, which was accompanied by patriotic music and images of North Korean landscape and military hardware, said the test had been ordered by the country’s leader, Kim Jong-un.

The explosion caused by a 6.3-magnitude earthquake felt in Yanji, China, about six miles (10km) from North Korea’s Punggye-ri nuclear test site in the north-east of the country.

South Korea’s meteorological administration estimated the blast yield at between 50 to 60 kilotons, or five to six times more powerful than North Korea’s fifth test in September last year.

Kim Young-woo, the head of South Korea’s parliamentary defence committee said later that the yield was as high as 100 kilotons. One kiloton is equivalent to 1,000 tons of TNT.

The previous nuclear blast in North Korea is estimated by experts to have been about 10 kilotons.

Sunday’s test, the first since Trump took office in January, offers further evidence that North Korea is moving perilously close to developing a nuclear warhead capable of being fitted on to an ICBM that can strike the US mainland.

Since it conducted its first nuclear test just over a decade ago, the regime has strived to refine the design and reliability of it weapons, as well as increasing their yield.

Hydrogen bombs are far more powerful than the atomic weapons Pyongyang is believed to have tested so far.

Trump also tweeted again shortly after noon, in apparent support of a new policy initiative announced by his treasury secretary, Steven Mnuchin, earlier in the day, where he called for any countries that trade with North Korea to be barred from trading with the US.

Mnuchin, also a member of Trump’s national security council, said on Sunday that he wanted to cut off North Korea’s economy because of the test.

“It’s clear that this behavior is completely unacceptable,” he told Fox News. “We have already started with sanctions but I’m going to draft a sanctions package that I’m going to send to the president for his strong consideration, that anybody that wants to do trade or business with them [North Korea] would be prevented from doing trade or business with us. People need to cut off North Korea, economically.”

When asked if the US would take a much tougher stance with Chinese financial institutions and companies in that regard, Mnuchin said: “We are going to strongly consider everything at this point.”

He refused to comment on “classified things” such as whether the test was a hydrogen bomb, not just an atomic bomb, and whether the US believed that North Korea had now miniaturized its nuclear capability to the point where it could put a nuclear warhead on an intercontinental ballistic missile.

“I can only say that the intelligence community has been doing an amazing job,” he said.

He said he had spoken to Trump about the issue that morning, but refused to clarify what the president meant when he said North Korea only understood “one thing”, or comment on the prospect of military action.

“The president has made it clear this is not the time for just talk, this is the time for action,” Mnuchin said. “Our objective will continue to be to de-nuclearize the peninsula … He will consider everything but we are not going to broadcast our actions. My focus right now is on additional economic sanctions. China has a lot of trade with them, there is a lot we can do to cut them off economically.”

China’s foreign ministry earlier said in a statement: “The Democratic People’s Republic of Korea has once again conducted a nuclear test in spite of widespread opposition from the international community. The Chinese government resolutely opposes and strongly condemns it.”

Before taking office, Trump declared North Korea would not be allowed to develop an ICBM capable of reaching the US mainland under his presidency.

After Pyongyang carried out two successful ICBM tests in July, Trump warned it would face “fire and fury like the world has never seen” if it made any further threats.

North Korea has since threatened to fire a salvo of missiles into the seas around the US Pacific territory of Guam, and fired a ballistic missile over Japanese territory for the firs time, ending US hopes that Trump’s threats had cowed Pyongyang into a pause in missile tests and a possible opening for talks.

In contrast to Trump, the US secretaries of defence and state, James Mattis and Rex Tillerson, have both emphasised that the US is relying on diplomacy and economic pressure in its approach to Pyongyang.

Complicating matters, Trump seems to be considering asking aides to prepare for US withdrawal from a free trade agreement with South Korea, it was reported on Saturday. Mnuchin stressed that “no decision has been made”.

Jeff Flake, a member of the Senate foreign relations committee, said: “I do not think that that would be good in any circumstances; it’s particularly troubling right now.”

Asked about Trump’s tweeted response to the nuclear test, Flake told CNN: “I have good confidence in our national security team and those who are advising the president. He does not have experience in this kind of situation. I’m confident that the people around the president are giving him good advice and he will take it – I sure hope he does.”

The Republican senator added: “I’ve had my concerns about statements from the president about Nato and foreign policy. We want someone who is measured and sober and consistent. Allies want to have that and our enemies need to have that.”

Flake said that Trump’s notorious threat last month to meet North Korean aggression with “fire and fury like the world has never seen” had not been not advisable.

“We have not slowed the advance of their nuclear program, but harsh rhetoric does not either,” he said. “Just about nothing we have done so far has slowed it down. It becomes a cliche to say there are no good options here, but there really are not. For those who believe we can simply strike and knock out their capability, they do not understand the situation there. But all options need to be on the table.”