Speaking on the condition of anonymity, a South Korean intelligence official told a local news station that “anthrax antibodies have been found in the North Korean soldier who defected this year”.
It is not known whether the soldier was exposed to or vaccinated against anthrax, the report revealed.
However, the official stated that the unnamed soldier developed the immunity to anthrax prior to his defection from the hermit kingdom.
Anthrax is an infection caused by the bacterium Bacillus anthracis and can occur in four forms: skin, lungs, intestinal, and injection.
The news has come as South Korean officials and independent weapons experts warned Pyongyang could be developing the biological weapons and could be ready to use anthrax.
Former assistant defence secretary Andrew Weber warned about how dangerous the weapons could be if developed by Kim Jong-un.
He said: “The Soviet Union did have warheads that were designed for biological weapons on long-range missiles.
“But it is really not necessary, you could deliver an anthrax attack in Los Angeles or Miami or New York, covertly and have a strategic impact and kill tens or thousands or hundreds of thousands of people.”
When asked how many people a “thumb-nail sized quantity of anthrax” could kill if sprayed in the right conditions, Mr Weber said maybe over ten thousand.
The North Korean regime rejected the claim as “groundless” and said that it was fulfilling its obligations under the Biological Weapons Convention (BWC) which prohibits the production or stockpile of biowarfare weapons.
Pyongyang also rejected the reports on the same day that a Japanese newspaper claimed the rogue state had already been successful in developing the weapons.
The article, which cites an anonymous source connected to South Korean intelligence, says: “North Korea has started experiments such as heat and pressure equipment to prevent anthrax from dying even at a high temperature of over 7,000 degrees generated at the time of ICBM’s re-entry into the atmosphere.
“In part, there is unconfirmed information that it has already succeeded in such experiments.”
In response, North Korea state media said: “The DPRK, as a state party to the BWC, maintains its consistent stand to oppose development, manufacture, stockpiling and possession of biological weapons.
“The more the US clings to the anti-DPRK stifling move, the more hardened the determination of our entire military personnel and people to take revenge will be.”
The comments come as the United Nations Security Council imposed tough new sanctions on North Korea after its continued missile testing.
The resolution seeks to ban nearly 90 percent of refined petroleum product exports to North Korea.
The resolution also bans exports of industrial equipment, machinery, transportation vehicles and industrial metals to North Korea.
Mr Trump tweeted: “The United Nations Security Council just voted 15-0 in favour of additional Sanctions on North Korea. The World wants Peace, not Death!”