North Korea has invited the entire US House of Representatives to take a tour of the Pyongyang Bio-technical Institute, a facility that biological weapons experts believe is intended to produce massive quantities of anthrax.

Speaking on Monday in state media, North Korean officials denied the biological weapons allegations, criticized US sanctions, and extended the rare invitation to American lawmakers.

"Come here right now, with all the 535 members of the House of Representatives and the Senate as well as the imbecile secretaries and deputy secretaries of the government who have made their voices hoarse screaming for new sanctions," a spokesperson for the National Defense Commission told the Korean Central News Agency (KCNA). "They can behold the awe-inspiring sight of the Pyongyang Bio-technical Institute."

The statement was the first official reaction since the US-Korea Institute at Johns Hopkins University published a report on July 9 alleging that the purported North Korean pesticide factory could produce anthrax. The report examined photos of Kim Jong-un touring the Pyongyang Bio-technical Institute, and analyzed the equipment visible in the background. The author of the report, Melissa Hanham, a senior researcher at the Center for Nonproliferation Studies, concluded that the "Institute is intended to produce military-size batches of anthrax."

Hanham told VICE News on Wednesday that North Korea's invitation to Congress was "more of a linguistic flourish than an earnest request."

"That being said," she added, "If they did ever want to open up the facility, I recommend inviting a team of qualified international inspectors, and sharing documents related to the procurement of the equipment at the site."

Hanham said previously that the images provided the clearest glimpse yet into North Korea's biological weapons program. "Very little is known about the origin of capability of North Korea's biological program," Hanham said. She concluded that the Institute likely produces pesticides as well as anthrax, noting that agricultural research is "an old and well-used cover for a biological weapons program."

After the report was published, Joel S. Wit, a former State Department official and a senior fellow at the US-Korea Institute at Johns Hopkins University, told VICE News that North Korea had "messed up."

"If you're a technical expert, it's clear looking at this facility that it can be used for biological warfare, particularly anthrax," he said. "The science is not in dispute."