President Joe Biden says North Korea has not responded to a US offer of Covid vaccines, as the country battles its first acknowledged outbreak.
Nearly 2.5 million people have been sickened by "fever" in North Korea and it is under a nationwide lockdown, according to the country's state media.
It is thought to be particularly vulnerable because it has little testing or vaccine supply.
Mr Biden announced the offer at a press conference in South Korea.
"We've offered vaccines, not only to North Korea but to China as well, and we're prepared to do that immediately," Mr Biden said in a joint appearance with South Korean President Yoon Suk-yeol.
"We've got no response," he added.
The isolated regime of North Korea has previously turned down offers of vaccines from Covax, the global vaccine-sharing scheme, and from South Korea, as well as reportedly declining other offers.
Instead it claimed to have successfully kept Covid out of the country by sealing its borders, although experts believe the virus has been present there for some time.
State media has recommended remedies such as herbal tea, gargling salt-water and taking painkillers such as ibuprofen, while the country's leader, Kim Jong-un, has accused officials of bungling the distribution of national medicine reserves.
China is also struggling to control a wave of infections from the highly transmissible Omicron variant, with tens of millions of people under some form of lockdown.
At the news conference in the South Korean capital, Seoul, President Biden said he was willing to meet Mr Kim under the right circumstances.
"It would depend on whether he was sincere and whether he was serious," Mr Biden said.
His predecessor, Donald Trump, held a historic summit with Mr Kim in Singapore in 2018 and became the first US president to set foot in North Korea the following year.
But two years ago, Mr Kim questioned whether there was any need to continue "holding hands" with the US.
The US and South Korean presidents also agreed to deploy American weapons if necessary to deter North Korea and to increase military drills – which had been scaled down in recent years in an effort to reduce tensions.
North Korea fighting Covid with tea and salt water
N Korea has confirmed Covid: What's likely to happen?
Over a million Covid cases feared in North Korea
North Korea questions need to 'hold hands' with US
No let up in battle for key eastern Ukraine city
Qatar accused of under-reporting heat deaths. VideoQatar accused of under-reporting heat deaths
Cost of living: The shock of rising prices in Japan
The women photographing Australia's climate crisis. VideoThe women photographing Australia's climate crisis
The voice that touched millions of Indian love stories
India's loan scam apps leave victims terrified
What to know about the 6 January riot hearings
Qatar accused of under-reporting heat deaths. VideoQatar accused of under-reporting heat deaths
Cost of living: The shock of rising prices in Japan
China's plans to go to the Moon, Mars and beyond
Why India's wheat export ban matters to the world
Ros Atkins On… Saudi Arabia’s $2bn golf series. VideoRos Atkins On… Saudi Arabia’s $2bn golf series
The 12 best films of 2022 so far
From Top Gun: Maverick to Turning Red and Everything Everywhere All at Once
Switzerland's ingenious cooling caves
When fridges didn't exist, locals had to find other ways to keep food cool
Why people believe their own big lies
The role self-deception plays in leading people astray
© 2022 BBC. The BBC is not responsible for the content of external sites. Read about our approach to external linking.
COVID-19
Surviving The 2nd Wave of Corona
‘This too shall pass away’ this famous Persian adage seems to be defeating us again and again in the case of COVID-19. Despite every effort