A new report from the Belfer Center for Science and International Affairs at Harvard’s Kennedy School states that North Korea is building up its inventory of biological weapons, including weaponized strains of anthrax and smallpox designed to cause mass casualties in civilian populations.

The report, entitled “North Korea’s Biological Weapons Program: The Known and the Unknown,” stipulates that many details remain unknown because so much of North Korea’s agricultural and medical equipment can also be used for bio-weapons (BW) production. Dictator Kim Jong-un’s interest in developing biological pesticides instead of the more common chemical variety may have a sinister hidden purpose.

The report mentions one problem with assessing the true nature of the activities at potentially dual-use facilities is that North Korea does not necessarily conform to international safety standards, so the protective systems that would normally be spotted at a secret bio-weapons lab might not be present in their facilities. Conversely, the authors concede that Pyongyang might be waging a bit of information warfare by subtly hinting it has a much more advanced biological warfare program that it actually possesses.

“Limited information on North Korea’s BW program leads to a low threat perception that may undermine preparation and response efforts,” the Belfer Center report warns.

The Belfer Center’s historical background notes that North Korea publicly blamed various disease outbreaks in the Fifties on bio-warfare attacks by the United States, giving the regime of the current dictator’s grandfather an excuse to work on biological weapons of its own, not to mention plenty of sick people to culture the diseases from. Although Pyongyang generally denies the existence of this program, South Korean intelligence believes it began producing weapons-grade biological agents in the Eighties.

A crucial 2000 white paper from the South Korean defense ministry indicated North Korea was most interested in developing anthrax and smallpox weapons but has also experimented with botulism, cholera, the plague, yellow fever, and staph, among others. As recently as 2015, a joint U.S.-South Korean investigation concluded North Korea has at least 13 pathogens in its inventory, and “it is possible that it would use them in bioterrorism or in an all-out war.”

A vital lingering question is whether North Korea has weaponized the biological agents in its possession to the point where they could be deployed with missiles or drone aircraft. This would require stabilizing the agents enough to deploy them into targeted environments without killing them, in a form that can be sprayed over a large area to produce the desired catastrophic effect.

Unfortunately, that is not as daunting a challenge as miniaturizing nuclear bombs enough to fit them inside missile warheads. “Agents like anthrax could cause mass casualties with only a small amount: only a few kilograms of anthrax, equivalent to a few bottles of wine, released into a dense city could kill 50 percent of the population,” the Belfer Center notes.

An easier method of deploying bio-weapons is probably available to the totalitarian regime: human distribution agents acting as suicide bio-bombers, disguising themselves as maintenance workers to spray pathogens disguised as cleaning fluids or contaminating city water supplies. “North Korea has 200,000 special forces; even a handful of those special forces armed with BW would be enough to devastate South Korea,” the report points out.

Biological weapons deployed in this manner might fit better into North Korea’s long-term strategy than nuclear weapons. The report speculates the North might launch bio-weapons attacks in South Korea to “disrupt society and create panic, incapacitate societies, and/or cause a significant military diversion” at the beginning of a conventional military invasion intended to unite the peninsula under Pyongyang’s control. This would have the advantage of decimating the South Korean population without destroying valuable infrastructure Pyongyang would like to seize.

It might also crucially delay forceful responses from Western powers, as the North Koreans would doubtless claim they had nothing to do with the mysterious plague running wild through South Korean cities. Biological warfare has a unique aspect that distinguishes it from nuclear or chemical weapons: a mass casualty attack could be well underway, inflicting enormous stress on a society and causing widespread panic, before investigators conclusively prove it is an attack, or determine who launched it.

The Belfer Center recommends more comprehensive vaccinations for South Korean troops as a protective measure, noting they are not currently vaccinated against anthrax and smallpox due to a shortage of vaccines, and the U.S. military does not have enough of a surplus to cover all of South Korea’s military. Also, the international community is advised to keep a close eye on North Korea’s bio-pesticide and fertilizer programs and be careful about providing training or equipment for humanitarian purposes that could be diverted to biological weapons research. This will be particularly important as genetic engineering technology grows more widespread.

A key incident cited several times in the report occurred at the Osan Air Force base in 2015, when a U.S. Army laboratory accidentally distributed live samples of anthrax during at a training exercise. North Korea hysterically portrayed the incident as a botched bio-weapons attack against them; the Belfer Center authors take it as a sign that communication between governments and security procedures for dangerous biological agents needs to be improved. Unfortunately, the incident also generated public resistance in South Korea to the deployment of BW equipment, including much-needed defensive systems.

The greatest challenges outlined by the report are the difficulty of either gaining solid information about North Korea’s activities or communicating effectively with the Kim regime. Information does not flow easily either in, or out, of the rogue Communist nation. It is difficult to gather reliable intelligence about the extent of North Korea’s biological weapons program, and unlike its nuclear weapons or ballistic missile programs, there are no telltale underground earthquakes or missiles streaking through Japanese airspace. Conversely, engaging North Korea in the sort of medical dialogue that might convince the regime not to meddle with BW—often seen as the poor man’s nuke, because they are deceptively easy to cultivate—is not easy.

“Overall, the goal of the international community should be to simultaneously gather more information about North Korea’s BW capability and reduce this threat posed by North Korea,” the report concludes. “It should not be comforted by the scarcity of information on the program, but should instead redouble efforts to better understand the threat and prepare to respond to it.”