Image caption The anthrax vaccine has been given to adults thought to be at risk of exposure to biological weapons

A US presidential commission has paved the way for testing an anthrax vaccine on children, prompting criticism that participants would be "guinea pigs".

But the bioethical issues report said researchers would have to overcome many hurdles before conducting any trial.

Health and Human Services Secretary Kathleen Sebelius must decide whether to act on the paper's recommendations.

An earlier biodefence commission said in 2011 that a vaccine should be developed for children.

The National Biodefence Science Board said at the time that any such study would need approval from a bioethics panel first.

One anthrax vaccine, BioThrax, is available for sale in the US. Drug-maker Emergent BioSolutions reported $215.9m (£142.8m) in sales of the vaccine in 2012.

Video-game scenario

Panel chairwoman Amy Gutmann said: "We have to get this precisely right," speaking at a news conference on Tuesday.

She added that "many significant steps would have to be taken" before a trial on children would be allowed to proceed.

But Ms Gutmann said the US must "develop the knowledge needed to save children's lives" if an anthrax attack ever occurred.

The chairwoman said striking the right balance of keeping children safe while understanding what a safe dose of the vaccine might be, made this "one of the most difficult ethical reviews a bioethics board has ever conducted".

Some activists said the Presidential Commission for the Study of Bioethical Issues should have rejected the idea of a trial on children altogether.

Vera Sharav, founder of the Alliance for Human Research Protection, said a trial would cause "moral harm" to the nation and suffering for children.

The issue came up in 2011 when a video game called Dark Zephyr portrayed an anthrax attack on a city modelled on San Francisco. It posed the question of whether children should be vaccinated in the event of an attack.

So far, the anthrax vaccine has been given to about 2.9 million adults - mostly members of the armed forces who were thought to be at risk of exposure to biological weapons in Iraq - and studies on animals.