TOKYO (AP) — In these days of infection and fear, a recent propaganda photo sums up the image North Korea wants to show the world, as well as its people: Soldiers with black surgical masks surround leader Kim Jong Un, ensconced in a leather overcoat and without a mask as he oversees a defiant military drill.

As a new and frightening virus closes in around it, North Korea presents itself as a fortress, tightening its borders as cadres of health officials stage a monumental disinfection and monitoring program.

That image of world-defying impregnability, however, may belie a brewing disaster.

North Korea, which has what experts call a horrendous medical infrastructure in the best of times, shares a porous, nearly 1,450-kilometer (900-mile) border with China, where the disease originated and has since rapidly spread around the world. The North's government has also long considered public reports on infectious disease — or, for that matter, anything that could hurt the ruling elite — matters of state secrecy.

This has raised fears that North Korea, which claims zero infections, may be vastly unprepared for a virus that is testing much more developed countries across the globe — and even that infections could already be exploding within its borders.

“Unfortunately, the international community has no idea if the coronavirus is spreading inside North Korea,” said a recent report by Jessica Lee, an East Asia expert at the Quincy Institute for Responsible Statecraft, a think tank in Washington. “The fact that we know nothing about the level of infection or deaths within North Korea is extremely problematic and, left unchanged, could have serious public health implications.”

North Korean media, meanwhile, are filled with self-described examples of ultra-vigilance — as well as a sense of urgency.

Calling its anti-virus campaign a matter of “national existence,” the North has banned foreign tourists, delayed the school year, quarantined hundreds of foreigners and thousands of locals who’ve traveled abroad, shut down nearly all cross-border traffic with China, intensified screening at entry points, and mobilized tens of thousands of health workers to monitor residents and isolate those with symptoms.

A parade of media photographs show North Korean doctors, scientists and health workers in masks, paper hats and protective clothing, discussing matters of science, or disinfecting public transportation, or planning ways to further protect citizens.

"No special cases must be allowed within the state anti-epidemic system," Kim, emerging recently from a prolonged period out of the public spotlight to oversee a politburo meeting on the virus, said, according to state media. Officials must “seal off all the channels and space through which the infectious disease may find its way.”

On Monday, Kim's military fired unidentified projectiles into the sea, weapons tests apparently aimed, in part, at showing that all's well amid outside worries about an outbreak in the North.

Despite the bravado, there are rising doubts that North Korea has dodged the virus.

Some North Korea monitoring groups, which claim to have a network of sources inside the nation, recently said that there are virus patients and deaths in North Korea, a claim the South Korean government couldn’t confirm.

“I’m 100% sure that North Korea already has infected patients,” said Nam Sung-wook, a North Korea expert at South Korea’s Korea University who served as president of the Institute for National Security Strategy, a think tank affiliated with South Korea’s main spy agency.

If North Korea had an outbreak similar to what’s happening in South Korea, the world’s hardest-hit country aside from China, it would cause serious turmoil because of a chronic lack of medical supplies and medicine, Nam said.

“North Korea would be helpless,” he said.

Some analysts believe that North Korea’s strong moves to shut down border areas with China, its only major ally and aid benefactor, signal that the virus has already spread into the nation from China, which has had more than 80,000 cases.

There is usually heavy border traffic between the two countries, and tens of thousands of North Koreans were believed to be working in China before a U.N. order for Beijing to send them back home expired in December. It’s unknown how many of them have returned home.

There have been growing outside calls for North Korea to open up about what’s going on inside its borders.

The U.N. Special Rapporteur on human rights in North Korea, Tomás Ojea Quintana, urged North Korea to “allow full and unimpeded access to medical experts and humanitarian actors, and relax restrictions on access to information. Further isolation of the country is not the answer.”

Ojea Quintana said that many North Koreans, especially in the countryside, lack proper access to health services, water and sanitation, and that more than 43% of the population is undernourished.

The United States also expressed worry about North Korea's vulnerability to the viral outbreak and said it was ready to support efforts by aid organizations to contain the spread of the illness in the impoverished nation.

An epidemic in North Korea, which experts say has a chronic lack of medical supplies, could further shake an economy battered by U.S.-led sanctions over its nuclear weapons and missile program. That, in turn, could quicken the depletion of the North's foreign currency reserves by choking off income from tourism and smuggling.

Decreased trade with China could also dry up the goods going to North Korea’s informal private markets, which have emerged as a big part of the national economy following the collapse of the state rationing system during a devastating famine in the 1990s, experts say.

And the country’s intensified anti-virus efforts could potentially hamper Kim's ability to mobilize his people for labor on major development and tourist projects, said Lim Soo-ho, an analyst from South Korea’s Institute for National Security Strategy think tank.

Despite a big economic hit to many North Koreans, however, the elite may survive a serious outbreak.

“North Korea has a powerful control over its people, and that was how it maintained its leadership when 2 to 3 million people died during ‘the arduous march period,’” Oh Gyeong-seob, an analyst at Seoul’s Korea Institute for National Unification, said, referring to the North Korean euphemism for the 1990s famine.

“Public dissatisfaction with Kim Jong Un will grow, but not at a level that will deal him a critical blow,” Oh predicted.

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Associated Press writers Hyung-jin Kim and Kim Tong-hyung in Seoul, South Korea, contributed to this report.

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Foster Klug, AP's news director for the Koreas, Japan, Australia and the South Pacific, has covered North Korea since 2005. Follow him at www.twitter.com/apklug