Federal cellphone guidelines for consumers could undergo "tweaks" after a major government study found a link between tumors and exposure to cellphone-type radiation in rats, according to a head of the agency that oversaw the study.

John Bucher, the associate director of the U.S. National Toxicology Program, said the decision will ultimately be up to other agencies like the Food and Drug Administration or the Federal Communications Commission (FCC).

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"If anything there may be some tweaks to these recommendations. We don't know at this point," he said on a conference call Friday.

The rats in the study were exposed to near-constant levels of radio frequency radiation. While the waves are similar to those emitted by cellphones, the rats were exposed to much heavier levels than is associated with typical cellphone use.

Bucher said it is still too early to say how the results translate to humans.

"This is a study that is looking at the biological plausibility of carcinogenic effects due to cellphone radiation," he said. "The direct translation of these finding to the way humans are using cellphones is not currently completely worked out. That is part of the evaluation that is going forward."

"This may have relevance; it may have no relevance," he added, noting that the study has not changed the way he uses a cellphone.

The FCC said it had been briefed on the study and noted that scientific evidence always informs its work on the matter.

The study of more than 7,000 animals ranged over two years. Partial results were released Friday because they help support a 2011 study by the World Health Organization that caused the group to classify cellphone radiation as potentially cancer causing.

The amount of radio frequency absorbed into the head of a person using a mobile phone is called the "specific absorption rate." The FCC sets that limit at 1.6 watts per kilogram averaged over a gram of tissue. The limit for full-body exposure — similar to what the rats received — is far lower.

The rats in the study were exposed to 1.5 to 6 watts per kilogram for nine hours every day. The study concluded that the development of tumors in some of the animals was likely a result of the exposure to full-body radiation.

CTIA, a large trade group representing the wireless industry, said it is still reviewing the findings. But the group noted that numerous studies have previously found "no established health effects from radio frequency signals used in cellphones."