North Korea began tests to load anthrax onto its intercontinental ballistic missiles, a report said Tuesday.

Bloomberg reported Japan’s Asahi Shimbun newspaper cited an unidentified person connected to South Korea’s intelligence services saying the testing involved making sure the anthrax was capable of surviving the high temperatures generated when the missiles re-enter the Earth’s atmosphere.

According to the Centers for Disease Control and Prevention, the deadly infection-causing bacteria would be one of the biological agents most likely to be used in case of a bioterrorist attack. Reports by South Korea previously stated the North was capable of producing biological agents such as anthrax and smallpox that could be used as a part of biological warfare.

The North was also thought to be among the world's largest possessors of chemical weapons, ranking third after the United States and Russia, according to the Nuclear Threat Initiative (NTI), a non-profit organization aiming at protecting lives and the environment from nuclear, biological, radiological, chemical, and cyber dangers. In 2012, the South Korean Ministry of National Defense estimated North Korea possessed between 2,500 and 5,000 metric tons of chemical weapons.

Although North Korea is party to both the Biological and Toxin Weapons Convention and the Geneva Protocol, it is suspected of maintaining an ongoing biological weapons program.

Several individuals including North Korean defectors as well as assessments by the U.S. and South Korean governments estimated the North began acquiring biological weapons as early as the 1960s, under the orders of Kim Il Sung.

The report by NTI also stated North Korea was capable of indigenously producing other agents of biological warfare including Variola major (smallpox), Francisella tularensis (rabbit fever), and Bunyaviridae Hantavirus (Korean hemorrhagic fever).

The report about the North’s testing of anthrax came after the U.S. published its National Security Strategy, a document that said Pyongyang was "pursuing chemical and biological weapons which could also be delivered by missile.”

“North Korea — a country that starves its own people — has spent hundreds of millions of dollars on nuclear, chemical, and biological weapons that could threaten our homeland,” the report said.

Rebecca Hersman, a former Defense Department deputy assistant secretary for countering weapons of mass destruction, was quoted in a Washington Post article speaking about the country’s bio-weapon program: “North Korea is bad enough when you’re talking about their nuclear and missiles program. But I think we ignore their chemical and biological programs truly at our own peril.”

The threat of an impending war with North Korea intensified after the country’s state television reported last month it launched a new intercontinental ballistic missile, Hwasong 15, which is a nuclear-capable weapon that could reach the entire continental U.S.

Secretary of State Rex Tillerson also announced a new international group Tuesday to increase the pressure on North Korea for a diplomatic solution to the global crisis over the regime's growing nuclear and ballistic missile programs.