(CNN) -- Details of a genetically altered strain of the deadly avian flu virus are "a grave concern" to public safety and should be kept under wraps, a federal advisory board declared Tuesday.
In a letter released by the journals Science and Nature, the 23-member National Science Advisory Board for Biosecurity said the data behind a new strain of the virus can be used to help prepare for a possible future outbreak. But the board recommended the researchers' findings be published without "methods or details" that could be used by terrorists to produce a biological weapon.
"This is an unprecedented recommendation for work in the life sciences, and our analysis was conducted with careful consideration both of the potential benefits of publication and of the potential harm that could occur from such a precedent," the panel wrote. "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 mammal-adapted influenza A/H5N1 viruses for harmful purposes."
The letter restates concerns first raised in December, after reports that scientists in Wisconsin and the Netherlands each created a strain of the influenza virus that is both highly lethal and easily transmitted between ferrets -- the animals that most closely mimic the human response to the flu.
A paper by the Dutch researchers was to be published in the journal Science, while the University of Wisconsin study was to be published in the journal Nature. Both journals have already agreed to postpone publication. But airing detailed results "represent(s) a grave concern for global biosecurity, biosafety, and public health," the NSABB concluded.
"Although scientists pride themselves on the creation of scientific literature that defines careful methodology that would allow other scientists to replicate experiments, we do not believe that widespread dissemination of the methodology in this case is a responsible action," they wrote.
But researchers involved in the bird-flu studies say censoring their papers would make it harder for scientists to share information while doing little to deter potential terrorists.
"The logic in this work is sufficiently obvious that virologists could perform experiments similar to ours even if our method is not published," the Dutch team wrote in Science last week.
Scientists and public health officials have long feared that the Asian bird flu virus, which now rarely infects people, could become a human-to-human disease. The flu has killed about 60% of the people who have contracted it since its discovery in 1997.
CNN's Miriam Falco contributed to this report.