US National Security Adviser HR McMaster has claimed that “all options are on the table” when it comes to dealing with the threat of North Korea.
Responding to what is believed to be a failed ballistic missile test by the Asian nation in the early hours of Sunday, Lt General McMaster said that the latest test "fits into a pattern of provocative and destabilising and threatening behaviour on the part of the North Korean regime".
With US Vice President Mike Pence also touching down in Seoul in South Korea, it is clear that US officials are making a concerted diplomatic push to try and get the situation in North Korea under control and reassure allies in the region.
General McMaster was speaking from Afghanistan, where he was due to meet with Afghan officials in Kabul. That visit follows the use by the US military of the largest non-nuclear weapon they have ever dropped in combat, the so-called "mother of all bombs," which destroyed a network of tunnels used by Isis in Afghanistan.
Destroying Isis was the main foreign policy aim of US President Donald Trump when he came into office earlier this year, but his administration now finds itself at the centre of a number of international crises, including the conflict in Syria, and new aggression from North Korea. This is seemingly at odds with Mr Trump's isolationist rhetoric on the campaign trail where he espoused a policy framework based on the slogan 'America First'.
The chain of events that led to such frantic diplomatic efforts began in Syria almost two weeks ago, when an apparent chemical gas attack on the Syrian town of Khan Sheikhun killed dozens of civilians and prompted the US to launch 59 missiles at a Syrian airbase. The US, along with the majority of the international community, blamed the gas attack on the forces of Syrian President Bashar al-Assad, although the regime - and their main supporters Russia - have denied it. Mr Trump said that the attack "crossed many lines" and he could not stand by, a U-turn on the previous policy reiterated just days previously that Mr Assad was not the priority in Syria, the jihadis of Isis were.
The US missile strike, which was labelled a "warning shot" against further use of chemical attacks by Mr Assad, signalled Mr Trump may be willing to shed his isolationist policies when the need arose, despite it threatening to alienate his core support. The strike on Syria was followed by the use of the GBU-42 Massive Ordnance Air Blast (MOAB) bomb on Isis positions in Afghanistan, with the dropping of the weapon also likely a signal to North Korea - whose rhetoric over the threat of war in the Asia-Pacific region had itself been escalating.
In light of all these moves, a strong US response to North Korea had been expected - particularly as a military test, potentially a nuclear one, had been expected on the weekend of North Korea staging a massive military parade celebrating the birth of its state founder. General McMaster made clear that it was working with China - who provides the majority of supplies to North Korea and try and resolve the aggression by North Korea.
“There is an international consensus now, including the Chinese leadership, that this is a situation that just cannot continue,” he said
In the UK, Foreign Secretary Boris Johnson tweeted: “I strongly condemn the latest North Korean missile launch. They must stop these belligerent acts and comply with UN resolutions.”
Such US cooperation with China makes a softening of the Trump administration's stance on China - with the US President having previously used China as one of his main scapegoats over changes to US trade practices that Mr Trump would oversee once in office.
Mr Trump has previously accused the country of apparent currency manipulation that leaves the leaves the US at a disadvantage on trade.
However, Mr Trump acknowledged China's help with the North Korean issue on Sunday, linking it to a softer line taken on China's management of its currency. “Why would I call China a currency manipulator when they are working with us on the North Korean problem? We will see what happens!” he said on Twitter - reversing his campaign rhetoric.
China's top diplomat, Yang Jiechi, and US Secretary of State Rex Tillerson also exchanged views on the “situation on the Korean peninsula” by phone, China's official Xinhua News Agency said. Mr Yang said the two sides should maintain dialogue.
General McMaster, in remarks in ABC's This Week news programme, made clear that the US would be looking to resolve the Issue peacefully. Former Conservative foreign secretary Sir Malcolm Rifkind suggested that action from the US may have already taken place without the need for a direct military confrontation “[The missile] could have failed because the system is not competent enough to make it work, but there is a very strong belief that the US - through cyber methods - has been successful on several occasions in interrupting these sorts of tests and making them fail,” Sir Malcolm told the BBC on Sunday.
But in a further tweet, Mr Trump referenced the military might of the US, following the line of officials in recent days that the country may not be afraid to use more direct methods in the face of further provocation - as in Syria and Afghanistan.
"Our military is building and is rapidly becoming stronger than ever before. Frankly, we have no choice!" Mr Trump said.
South Korea said the North's latest show of force “threatened the whole world” but a US foreign policy adviser travelling with Mr Pence on Air Force Two sought to defuse some of the tension, saying the test of what was believed to be a medium-range missile had come as no surprise.
“We had good intelligence before the launch and good intelligence after the launch,” the adviser told reporters on condition of anonymity.
“It's a failed test. It follows another failed test. So really no need to reinforce their failure. We don't need to expend any resources against that.
"It wasn't a matter of if, it was a matter of when. The good news is that after five seconds it fizzled out.”
Mr Pence, addressing an Easter service with American troops in South Korea, said the US commitment to South Korea was unwavering.
“Let me assure you under President Trump's leadership, our resolve has never been stronger. Our commitment to this historic alliance with the courageous people of South Korea has never been stronger.”
Mr Pence was beginning a 10-day trip to Asia in what his aides said was a sign of US commitment to its ally in the face of rising tension. The US nuclear-powered Carl Vinson aircraft carrier strike group is also heading to the region.
South Korea, which hosts 28,500 US troops and holds a presidential election on 9 May, warned of punitive action if the Sunday launch led to further provocation.
“North Korea showing a variety of offensive missiles at yesterday's military parade and daring to fire a ballistic missile today is a show of force that threatens the whole world,” South Korea's Foreign Ministry said in a statement.
Impoverished North Korea and the rich, democratic South are technically still at war because their 1950-53 conflict ended in a truce, not a peace treaty.
The North has warned of a nuclear strike against the United States if provoked. It has said it has developed and would launch a missile that can strike the mainland United States but officials and experts believe it is some time away from mastering the necessary technology, including miniaturising a nuclear warhead.
Earlier this month, the North launched a ballistic missile from the same region as the latest test, ahead of a summit between the United States and China in Florida to discuss the North's arms programme.
But that missile, which US officials said appeared to be a liquid-fuelled, extended-range Scud, only flew about 40 miles (60km), a fraction of its range before spinning out of control.
As for China, the nation has appeared increasingly frustrated with the North. It banned imports of North Korean coal in February, cutting off its most important export. China's customs department issued an order last week telling traders to return North Korean coal cargoes.
Agencies contributed to this report