Those soft fabric sleep positioners that anxious parents put in the crib to keep babies safely sleeping on their backs could be dangerous, even deadly, for little ones, the federal government warned Wednesday.

Citing 12 deaths, the Food and Drug Administration and the Consumer Product Safety Commission said parents, caregivers and others should not use the sleep positioners at all because of a suffocation risk.

The babies, ranging in age from one to four months, died when they suffocated in the positioner or became trapped between the positioner and the side of a crib and then suffocated. The deaths spanned the last 13 years.

Most of the babies suffocated after rolling from a side to stomach position, the agencies said in their joint announcement.

"In most instances, these products provide no real benefit and the risk of harm when they are used is significantly greater," cautioned FDA principal deputy commissioner Joshua Sharfstein, during a teleconference with reporters.

CPSC Chairman Inez Tenenbaum said her agency has received dozens of reports of babies who were placed on their backs or sides in the positioners and were later found in a potentially dangerous position inside the positioner or next to it.

The positioners are usually made of a soft cloth mat with a cushion on each side to hug or cradle the baby on her back. Marketed for babies ages six months and younger, positioners are promoted as a way to keep a young infant from rolling onto his tummy during sleep, or as a way to prevent sudden infant death syndrome or to ease acid reflux.

The American Academy of Pediatrics has long urged parents not to use positioners, saying there's no evidence that they help keep a baby in place or that they reduce the risk of SIDS.