Citing fears of an “unimaginable catastrophe,” a government-appointed board on Tuesday explained why it recently recommended censoring details of new research on deadly bird flu virus.

“Our concern is that publishing these experiments in detail would provide information to some person, organization, or government that would help them to develop similar ... viruses for harmful purposes,” the 23 voting members of the National Science Advisory Board for Biosecurity wrote in a statement published jointly Tuesday by the journals Science and Nature.

The potential harm of publishing the research on H5N1, or avian, influenza in full exceeded the potential benefits, the board wrote, adding its decision was unanimous.

“We do not believe that widespread dissemination of the methodology in this case is a responsible action,” they wrote.

Fears of bad actors spreading a mutant, highly transmissible virus suffuse the three-page note published by the board.

“The details of the research ... could enable someone to replicate the work in a short period of time,” wrote the chairman of the NSABB, Paul Keim, in a separate note published by the journal mBio.

In the experiments in question, university-based scientists in the Netherlands and Wisconsin created a version of the H5N1 virus that is highly lethal and easily transmissible between ferrets, the lab animals that most closely mirror human beings in flu research.

That work led to fears that the modified virus could also easily jump from person to person. Such transmissibility, which the board said could significantly raise the odds of a pandemic, has only rarely been seen in natural H5N1.

“If influenza A/H5N1 virus acquired the capacity for human-to-human spread ... we could face an epidemic of substantial proportions,” the board wrote.

The board compared the new research on H5N1 to the development of the atomic bomb in the 1940s. In that decade, physicists also confronted the dilemma of how much of their work to make public.

But some flu researchers say the board is making too many assumptions. The ferret work does not automatically imply that the new strain of the virus can be transmitted between people, said Daniel Perez, an influenza researcher at the University of Maryland in College Park.

Further, Perez said, only specialized laboratories could produce a mutated virus. “You would need much more than a fair amount of expertise — and then again, all you may have accomplished is to obtain a ferret-adapted virus, not a human-adapted virus.”

The research at Erasmus Medical Center in the Netherlands and the University of Wisconsin at Madison was performed to help prepare vaccines for mutations that might appear naturally in H5N1 viruses.

The board cannot prohibit publication of the research. But in December, Science and Nature agreed to at least temporarily abide by the board’s recommendation and delay publication.

On Jan. 20, the world’s top influenza researchers agreed to a self-imposed 60-day moratorium on new research on H5N1 to give the scientific and public health communities time to sort through the thorny issues raised by the request to withhold publication.

About 600 people, mostly in Southeast Asia, have become ill from the H5N1 virus since 1997. About 60 percent have died. In most cases, infection requires close contact with sick birds.

The high virulence of the virus makes it the most feared of any type of influenza. Since the virus surfaced, public health officials have worried that the virus might naturally mutate into a highly transmissible form that can quickly spread around the world.

The U.S. government created the NSABB after anthrax spread by letters killed five people in 2001. Before its December recommendation, though, it had never sought to censor a publication.