A senior World Health Organization official has said high levels of transmission of the coronavirus among unvaccinated people, such as in North Korea, creates a higher risk of new variants.
The isolated country, a WHO member, is grappling with its first acknowledged Covid-19 outbreak, fuelling concerns over a major crisis due to a lack of vaccines and medical infrastructure.
"Certainly it's worrying if countries ... are not using the tools that are now available," said WHO emergencies director Mike Ryan in response to a question about the outbreak in North Korea.
"WHO has repeatedly said that where you have unchecked transmission, there is always a higher risk of new variants emerging," he said.
At the same press briefing, WHO chief Tedros Adhanom Ghebreyesus also said he was "deeply concerned" about the spreading virus among an unvaccinated population with many underlying conditions.
The UN health agency has previously said North Korea has yet to inform it officially of the outbreak in an apparent violation of the country's legal obligations under the WHO's International Health Regulations.
Asked about how the WHO would respond, Dr Ryan said that the body was ready to help but had no power to interfere in a sovereign country.
It comes as North Korean military medics ramped up the distribution of medicines to fight the growing outbreak, state media said, with the number of reported cases of "fever" nearing 1.5 million.
North Korean leader Kim Jong-un has ordered nationwide lockdowns to try to slow the spread of the disease through the unvaccinated population.
He has deployed the military after what he has called a botched response to the outbreak.
Hundreds of personnel in camouflage uniforms from the Korean People's Army medical units were seen rallying in the capital Pyongyang in photos released by the official Korean Central News Agency (KCNA).
The military "urgently deployed its powerful forces to all pharmacies in Pyongyang City and began to supply medicines under the 24-hour service system", KCNA said.
Mr Kim had strongly criticised healthcare officials for their failure to keep pharmacies open.
North Korea's leader has put himself front and centre of the country's Covid response since its first case was announced last week, saying the outbreak is causing "great upheaval".
Authorities had reported more than 1.48 million cases of "fever" as yesterday evening, KCNA said, with the death toll at 56.
"At least 663,910 are under medical treatment," the agency said.
Authorities have stepped up media awareness campaigns and pharmaceutical factories have increased the production of medicines, KCNA reported.
North Korea has one of the world's worst healthcare systems, with poorly equipped hospitals, few intensive care units, and no Covid treatment drugs or mass testing ability, experts say.
"Most North Koreans are chronically malnourished and unvaccinated, there are barely any medicines left in the country, and the health infrastructure is incapable to deal with this pandemic," said Lina Yoon, senior Korea researcher at Human Rights Watch.
She urged the international community to offer medicines, vaccines and infrastructure to North Korea.
Pyongyang has so far not responded to an offer of help from Seoul, according to South Korea's unification ministry.
South Korea's new president Yoon Suk-yeol has taken a hawkish stance on his country's nuclear-armed neighbour, but told politicians yesterday that he would "not hold back" on aid -- if Pyongyang accepts.
Despite the Covid crisis, new satellite imagery has indicated North Korea has resumed construction at a long-dormant nuclear reactor.
The US and South Korea have warned that Kim is preparing to conduct another nuclear test -- the country's seventh.