Dutch scientists carried out the controversial research to genetically mutate the H5N1 strain of bird flu into a highly infectious "airborne" strain of human flu, saying the knowledge gained could be vital for the development of new vaccines and drugs.
But as the researchers propose to publish details of how they did it, some are arguing the information is too dangerous to be published.
"The fear is that if you create something this deadly and it goes into a global pandemic, the mortality and cost to the world could be massive," a senior scientific adviser to the U.S. government told the British newspaper The Independent, speaking on condition of anonymity.
"The worst-case scenario here is worse than anything you can imagine."
Scientists say the new strain of H5N1 -- created with just five mutations in two key genes -- has the potential to cause a devastating human pandemic that could kill tens of millions of people.
There is a serious possibility of information being misused if the full genetic sequence of the mutated virus were to be published in open scientific literature, they said.
"There are areas of science where information needs to be controlled," a scientist with the U.S. National Science Advisory Board for Biosecurity said. "The most extreme examples are, for instance, how to make a nuclear weapon or any weapon that is going to be used primarily to kill people. The life sciences really haven't encountered this situation before. It's really a new age."
"It's scary from a number of different angles. You want to have the vaccines and therapeutics in place, and you need to have as much information as you can about a particular virus, but you also worry about it from a biosecurity perspective."
The editor of the journal Nature said the publication was reviewing a paper sent to it by the Dutch researchers.
"I confirm that Nature is considering one of the two papers mentioned by the National Science Advisory Board for Biosecurity and are in active consultation with them," Editor-in-Chief Dr. Philip Campbell said in a statement.
"We have noted the unprecedented NSABB recommendations that would restrict public access to data and methods and recognize the motivation behind them.
"It is essential for public health that the full details of any scientific analysis of flu viruses be available to researchers. We are discussing with interested parties how, within the scenario recommended by NSABB, appropriate access to the scientific methods and data could be enabled," the statement said.