US President Joe Biden and South Korea's new President Yoon Suk-yeol signalled on Saturday an expanded military presence in response to the "threat" from North Korea, while also offering to help the isolated regime face a Covid-19 outbreak.
After meeting in Seoul on Mr Biden's first trip to Asia as president, the two leaders said that "considering the evolving threat posed by" North Korea, they agreed "to initiate discussions to expand the scope and scale of combined military exercises and training on and around the Korean peninsula".
The possible beefing up of joint exercises comes in response to the growing belligerence of North Korea ― which has carried out a blitz of sanctions-busting weapons tests this year ― as fears grow that leader Kim Jong-un will order a nuclear test during Mr Biden's visit to Asia.
Mr Biden and Mr Yoon also extended an offer of help to Pyongyang, which recently announced it is in the midst of a Covid-19 outbreak in a rare admission of internal troubles.
The two presidents expressed concern over the outbreak and said they "are willing to work with the international community to provide assistance" to North Korea to help fight the virus.
On Saturday, North Korean state media reported nearly 2.5 million people had been sick with "fever" with 66 deaths as the country "intensified" its campaign against the pandemic.
Mr Biden, while adding that he would not exclude a meeting with Mr Kim if he were "sincere", indicated the difficulty of dealing with the unpredictable dictator.
"We've offered vaccines, not only to North Korea but to China as well and we're prepared to do that immediately," he said at a press conference with Mr Yoon. "We've got no response."
Mr Yoon stressed that the offer of Covid aid was according to "humanitarian principles, separate from political and military issues".
Elected on a strongly pro-US message, Mr Yoon emphasised the need to reinforce South Korea's defences.
Mr Yoon said he and Mr Biden "discussed whether we'd need to come up with various types of joint drills to prepare for a nuclear attack".
Talks are also continuing on ways to "co-ordinate with the US on the timely deployment of strategic assets when needed", he said, reaffirming commitment to North Korea's "complete denuclearisation".
The strategic assets should include "fighter jets and missiles in a departure from the past when we only thought about the nuclear umbrella for deterrence", he said.
Any such deployments, or a ramping up of US-South Korea joint military exercises, is likely to enrage Pyongyang, which views the drills as rehearsals for invasion.
Mr Biden began the day by paying respects at Seoul National Cemetery, where soldiers killed defending South Korea, including many who fought alongside US troops in the Korean War, are buried.
He then held closed-door talks with Mr Yoon before the joint press conference and a state dinner.
A US official said that in addition to tensions over North Korea and the US-led campaign to punish Russia for invading Ukraine, Mr Biden's main focus on Saturday was establishing "a strong personal relationship" with Mr Yoon, who is less than two weeks into his presidency.
Like Japan, where Mr Biden flies on Sunday, South Korea is seen as a key player in US strategy to contain China and maintain what Washington calls the "free and open Indo-Pacific".
Mr Biden's Asia trip "is about demonstrating unity and resolve and strengthening the coordination between our closest allies", a senior US official told reporters on condition of anonymity.
In Japan, Mr Biden will meet Prime Minister Fumio Kishida and the emperor.
On Monday, he will unveil a major new US initiative for regional trade, the Indo-Pacific Economic Framework for Prosperity. A day later, he will join a regional summit of the Quad — a grouping of Australia, India, Japan and the US.
On arrival Friday in South Korea, Mr Biden accompanied Mr Yoon on a tour of a large Samsung semiconductor factory.
The microchips are a vital component in almost every piece of sophisticated modern technology, and South Korea and the US need to work to "keep our supply chains resilient, reliable and secure", Mr Biden said.
For the US leader, whose Democratic Party fears a possible trouncing in mid-term elections in November, snarled supply chains are an acute domestic political challenge, with Americans increasingly frustrated over rising prices and setbacks in the post-Covid pandemic recovery.
Mr Biden emphasised Samsung's decision to build a new semiconductor plant in Texas, opening in 2024.
In the southern US state of Georgia, the governor on Friday announced that South Korean auto giant Hyundai will build a $5.5 billion plant to produce electric vehicles and batteries.