Following accusations last week from U.S. experts claiming that North Korea is capable of mass-producing anthrax, Pyongyang challenged President Obama to send all 535 members of Congress to come inspect its bio-tech facility themselves.

"A thousand pairs of ears cannot match a pair of eyes," the spokesman for North Korea's National Defense Commission told state-run KCNA, reported AFP.

Suspicions were raised in the U.S. last week following the release of a research report by 38North, a blog run by the Johns Hopkins University U.S.-Korea Institute, which said that the North Korean pesticide facility is technologically equipped to produce military-sized batches of biological weapons, particularly anthrax.

The North Korean spokesman insisted the facility was used only to manufacture pesticides, and accused the U.S. government of spreading rumors about North Korea's weapons program.

"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," the spokesman said, according to AFP. "Then they can behold the awe-inspiring sight of the Pyongyang Bio-technical Institute."

In a separate English-language version of the KCNA report, a spokesman said the West is running a "smear campaign" with the intentions of kicking "off hysteria against [North Korea], denying stark reality."

"The South Korean puppet forces, sheltering in doghouses of the U.S., are fated to exist only when they bark at its prodding as they live on the crusts of bread thrown by it," the report said.

To come to the conclusion that the North has the ability to mass-produce anthrax, Melissa Hanham, a senior researcher at the Center for Nonproliferation Studies in Washington, examined a number of photographs published by North Korean state media last week.

She said the pictures show that Pyongyang has been importing dual-use equipment, which makes it difficult to identify their intended use.

"The modern equipment seen in the images reveal that North Korea is not only maintaining a biological weapons capability, but also has an active large-scale sanctions busting effort to illicitly procure the equipment for the Pyongyang Biotechnical Institute. This effort runs counter to international treaties, regimes and national laws that aim to prevent the spread of biological weapons, the equipment and chemicals used to make them and their means of delivery," Hanham wrote in the report.

"It is hard to avoid the conclusion that the Institute is intended to produce military-size batches of anthrax. If Pyongyang was interested only in food security, it could have procured Bt bio-insecticide legally and at a fraction of the cost. Instead, by choosing to illicitly import the dual-use equipment, North Korea is likely using the facility to maintain a latent [bio-weapons] capability - or worse - actively producing anthrax."

She concluded: "The bottom line is that regardless of whether the equipment is being used to produce anthrax today, it could in the near future."