US President Joe Biden and South Korea President Yoon Suk Yeol have said they will consider expanded military exercises to deter the nuclear threat from North Korea at a time when there is little hope of real diplomacy on the matter.
The announcement reflects a shift in direction by both leaders from their predecessors.
Former US president Donald Trump had considered scrapping the exercises and expressed affection for North Korean leader Kim Jong Un, and the last South Korean president, Moon Jae-in, remained committed to dialogue with Mr Kim to the end of his term despite being repeatedly rebuffed by the North.
Mr Biden said co-operation between the US and South Korea shows “our readiness to take on all threats together”.
North Korea, which has defended its nuclear weapons and missile development as a necessary deterrence against what it describes as US threats, could well respond angrily to Saturday’s announcement.
It has long described joint military exercises as rehearsals for an invasion, although the allies have portrayed the drills as defensive.
Mr Biden and Mr Yoon affirmed in remarks at a news conference that their shared goal is the complete denuclearisation of North Korea.
The US and South Korea said in a joint statement that they were committed to a “rules-based international order” following Russia’s invasion of Ukraine.
The statement is likely to set the stage for how the US and its allies will address any challenges with North Korea.
Yet Mr Biden also reiterated his offer of vaccines to North Korea as the coronavirus spreads at a dangerously fast speed through that country.
Asked if he would be willing to meet with Mr Kim, Mr Biden said that would depend on whether the North Korean leader was “sincere” and “serious”.
“Yes, we’ve offered vaccines, not only to North Korea but China as well,” Mr Biden said.
“We’re prepared to do that immediately. We’ve gotten no response.”
The division of the Korean peninsula after the Second World War has led to two radically different countries.
In South Korea, Mr Biden is touring factories for computer chips and next-generation cars in a democracy and engaging in talks for greater co-operation.
But in the North, there is a deadly coronavirus outbreak in a largely unvaccinated autocracy that can best command the world’s attention by flexing its nuclear capabilities.
Speaking to reporters aboard Air Force One as Mr Biden flew to South Korea, White House national security adviser Jake Sullivan said the US has co-ordinated with Seoul and Tokyo on how they will respond should the North conduct a nuclear test or missile strike while Mr Biden is in the region or soon after.
Mr Sullivan also spoke with his Chinese counterpart Yang Jiechi earlier in the week and urged Beijing to use its influence to persuade the North to cease the tests.
As part of a five-day visit in Asia, Mr Biden spent Saturday developing his relationship with Mr Yoon, who assumed office little more than a week ago.
In advance of the meeting, there have been worries in Seoul that Washington is slipping back to the Obama administration’s “strategic patience” policy of ignoring North Korea until it demonstrates seriousness about denuclearisation, an approach that was criticised for neglecting the North as it made huge strides in building its nuclear arsenal.
The US president opened on Saturday by laying a wreath at Seoul National Cemetery, wearing white gloves and a sombre expression as he also burned incense and then signed a guest book.
Mr Biden then greeted Mr Yoon at the People’s House for a nearly two-hour meeting and brief public remarks.
The pair will also hold a joint news conference and attend a leaders’ dinner at the National Museum of Korea.
In addition to North Korea, both leaders are keen to emphasise growing trade relations as two Korean industrial stalwarts – Samsung and Hyundai – are opening major plants in the US.
Mr Biden faces growing disapproval within the US over inflation near a 40-year high, but his administration sees one clear economic win in the contest with China for influence in the Pacific.
Bloomberg Economics Analysis estimates that the US economy will grow faster this year than China for the first time since 1976, a forecast that White House press secretary Karine Jean-Pierre credited to Mr Biden’s spending on coronavirus relief and infrastructure that led to faster job growth.
The national security event that is galvanising broader discussions between the two countries has been Russia’s invasion of Ukraine, a war that has led to an unprecedented set of sanctions by the US and its allies.
South Korea joined the US in imposing export controls against Russia and blocking Russian banks from the Swift payments system.
Its participation was key to stopping Russia’s access to computer chips and other technologies needed for weapons and economic development.
At the start of the administration, many White House officials thought that Mr Kim’s nuclear ambitions would prove to be perhaps the administration’s most vexing challenge and that the North Korean leader would aim to test Mr Biden’s mettle early in his time in office.
Through the first 14 months of Biden’s administration, Pyongyang held off on missile tests even as it ignored efforts by the administration to reach out through back channels in the hopes of restarting talks that could lead to the North’s denuclearisation in return for sanctions relief.
But the quiet did not last.
North Korea has tested missiles 16 separate times this year, including in March, when its first flight of an intercontinental ballistic missile since 2017 demonstrated a potential range including the entire US mainland.
The Biden administration is calling on China to restrain North Korea from engaging in any missile or nuclear tests.
Speaking on Air Force One, Mr Sullivan said Mr Biden and Chinese President Xi Jinping could hold a phone call in the coming weeks.
Mr Biden has fiercely criticised Beijing over its human rights record, trade practices, military harassment of the self-ruled island of Taiwan and more.
And while Mr Biden has made clear that he sees China as the United States’ greatest economic and national security competitor, he says it is crucial to keep the lines of communication open so the two powers can co-operate on issues of mutual concern.
North Korea is perhaps highest on that list.
White House officials said Mr Biden will not visit the Demilitarised Zone (DMZ) dividing the Korean peninsula during his trip – something that has become standard for US presidents during Seoul visits dating back to Ronald Reagan.
Mr Biden visited the DMZ in 2013 as vice president.
Mr Sullivan said the president’s decision to skip the stop this time was not driven by security concerns.
Instead, Mr Biden on Sunday will visit the Air Operations Centre’s Combat Operations Floor on Osan Air Base, south of Seoul.
The US sees it as one of the most critical installations in North East Asia.