Leading US health official Anthony Fauci on Wednesday rejected claims that the United States is censoring science by seeking to limit potentially dangerous bird flu information in major journals.

The controversy arose when two separate research teams -- one in the Netherlands and the other in the United States -- separately found ways to alter the H5N1 avian influenza so it could pass easily between mammals.

Until now, bird flu has been rare in humans, but particularly fatal in those who do get sick. H5N1 first infected humans in 1997 and has killed more than one in every two people that it infected, for a total of 350 deaths.

Based on fears that a deadly global pandemic could result if the mutant flu escaped a lab or if a terror group were to find out how to make it, a US advisory panel on Tuesday urged scientific journals to hold back key details.

The data "clearly has public health benefit but it has the potential to be used in nefarious ways by some people," said Fauci, who heads the National Institute of Allergy and Infectious Diseases.

The National Science Advisory Board for Biosecurity (NSABB), made up of 23 non-governmental experts, voted unanimously that studies should be published in the journals Science and Nature, but with limited information.

Fauci said that any "legitimate" researchers would be able to seek the full details for their own study.

"If their credentials are appropriate they will have access to that information. So it's not like classified information," he told AFP.

"It's only for those people who have a need to know and have a legitimate purpose for it, as opposed to just throwing it out there so that anybody can do whatever they want," he added.

"It's absolutely not censorship because if you are a scientist and you have the need to know... you will definitely get that information."

The two research teams were funded by grants from the National Institutes of Health, and are in the process of working out changes to their manuscripts with the journals Nature and Science.

Fauci also said that fears of what the mutant virus might do have been overblown. For instance, just because it could be passed easily between ferrets does not necessarily mean it could be as easily transmitted between humans.

"There is a little bit of an overreaction," he said, calling reports of a "monster virus" a "bit dramatic."

The real concern is that H5N1 might mutate in nature and become an influenza that humans could catch and transmit easily, so knowing what those flu features might look like is an important research and surveillance tool, he said.

"We could give that information to the people who are out of the field doing the surveillance, the health officials in Vietnam, Indonesia or China... so they will have a better chance of recognizing as the virus starts to evolve," he said.

"So the scientific question is very legitimate."

Fauci said the NSABB's request for redaction was the first time the advisory committee had made such an appeal, and acknowledged that it was not popular in all corners of the science world.

"There are many scientists who don't agree with the committee. So we need to re-look at what the rational for that decision was, so we can all get together in an open and a transparent way, come up with some more concrete guidelines of what needs to be looked in these cases," he said.

"That is going to trigger some interesting dialogue, I believe."