Two top scientific journals said Tuesday they were mulling whether to publish details of a man-made mutant killer flu virus that has sparked concerns of mass deaths if it were released.

A US government's science advisory committee urged the US journal Science and the British journal Nature to withhold key details so that people seeking to harm the public would not be able to manufacture the virus that could cause millions of deaths.

The virus in question is an H5N1 bird flu strain that was genetically altered in a Dutch lab so it can pass easily between ferrets.

That means it is likely contagious among humans for the first time, and could trigger a lethal pandemic if it emerged in nature or were set loose by terrorists, experts have said.

The National Science Advisory Board for Biosecurity reviewed two scientific papers relating to the findings and recommended that the journals "make changes in the manuscripts," a statement said, warning of an "extremely serious global public health threat."

"Due to the importance of the findings to the public health and research communities, the NSABB recommended that the general conclusions highlighting the novel outcome be published, but that the manuscripts not include the methodological and other details that could enable replication of the experiments by those who would seek to do harm."

The H5N1 strain of avian influenza is fatal in 60 percent of human cases but only 350 people have so far died from the disease, largely because it cannot, yet, be transmitted between humans.

Science and Nature said they were considering the US government's non-binding request.

"At the same time, however, Science has concerns about withholding potentially important public health information from responsible influenza researchers," editor-in-chief Bruce Alberts said.

Scientists could benefit from knowing about the virus because it could help speed new treatments to combat this and other related lethal forms of influenza, he added.

"Many scientists within the influenza community have a bona fide need to know the details of this research in order to protect the public, especially if they currently are working with related strains of the virus," Alberts wrote.

"Science editors will be evaluating how best to proceed," he added, asking for more clarification on how the government would make the information available to "all those responsible scientists who request it."

A spokeswoman for the American Association for the Advancement of Science, which publishes Science, told AFP a decision was expected in two weeks.

Nature's editor-in-chief, Philip Campbell, said he was considering one of the two papers for publication and was in "active consultation" on the matter.

"We have noted the unprecedented NSABB recommendations that would restrict public access to data and methods and recognize the motivation behind them," he said.

"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 Dutch research team was led by Ron Fouchier at Rotterdam's Erasmus Medical Center. The team said in September it had created a mutant version of the H5N1 bird flu virus that could for the first time be spread among mammals.

Fouchier said his team had discovered that transmission of the virus was possible between humans "and can be carried out more easily than we thought."

One paper under consideration is by Fouchier's team, and the other is by a team of virologists at the University of Wisconsin and the University of Tokyo that reportedly showed similar results.

NSABB chair Paul Keim, a microbial geneticist, told the AAAS Science Insider report last month that he had huge concerns about the potential havoc the man-made virus could unleash.

"I can't think of another pathogenic organism that is as scary as this one," Keim was quoted as saying. "I don't think anthrax is scary at all compared to this."