The FDA said it did not have enough information to make an assertion about cloned sheep.

The ruling was the latest twist after years of debate over the reproductive technology, which advocates say will provide consumers with top-quality food by replicating prized animals that can breed highly productive offspring.

The cloning industry, made up so far of only a handful of firms, expects that it will be the offspring of cloned animals, not the costly clones themselves, that would eventually provide meat or milk to US consumers.

There are currently about 570 cloned animals in the United States, but the livestock industry has so far followed a voluntary ban on marketing food from the animals.

Yet even as the FDA unveiled its final assessment, the Agriculture Department asked the cloning industry to extend that ban during a "transition" period.

USDA said it will reach out to livestock producers, cloning firms, trading partners and others to lay a smooth path for selling clone-derived food in the future.

It could take four or five years before consumers are able to buy products derived from cloned animals.

FUTURE HURDLES?

While scientific studies appear to support the cloning industry's claims that the technology is safe, the topic remains controversial even within the agriculture industry.

Some dairy firms oppose cloning, betting that consumers will shun goods they see linked to cloning technology.

Others believe that more investigation is needed before concluding that cloning is safe -- especially after a year in which consumer confidence was marred by numerous food scares -- or oppose it on moral or religious grounds.

"Despite widespread public disapproval, FDA is not planning to require labeling of products from cloned animals, keeping already wary consumers in the dark," Food and Water Watch, an advocacy group, said in a statement.

Greg Jaffe, director of biotechnology at the Center for Science in the Public Interest, says the cloning industry must now convince the public why cloning is useful.

"Just because the technology is safe, it doesn't mean that as a society there is reason to embrace it," he said.

Jaffe expects Congress or some states may try to impose additional restrictions on marketing or labeling.

The Senate has passed a measure that would delay FDA approval until the completion of more studies.

Several major food companies quickly stated that they are not signing up, at least right away. Tyson Foods Inc, the largest US meat producer, said on Tuesday it has no immediate plans to buy cloned livestock.

The FDA cloning decision comes as biotechnology becomes an ever more important part of global agriculture.