WASHINGTON >> Two government studies that bombarded rats and mice with cellphone radiation found a weak link to some heart tumors, but scientists and federal regulators say don’t worry — it is still safe to use your device.

Previous studies of cellphone users had found little reason for concern, but the newest research took a closer look at the effects of super-high doses in animals to address some lingering questions that could not be tested on humans.

The rat study released today found a small increase in an unusual type of heart tumor in male rats but no other significant problems in females or in a separate study of mice. In particular, scientists could not find hard evidence for concern about brain tumors.

The lead author of the research, John Bucher of the National Institute of Environmental Health Sciences, is not changing his cellphone use or advising his family to.

Adding to the confusion about how to weigh these results, the same study that found heart tumors nonetheless showed that the radiated rats somehow lived longer than the control group that was not radiated.

The findings about the rare nerve-tissue tumor discovered in the hearts of male rats do not translate directly into a concern for humans, Bucher said.

Bucher’s agency conducted the $25 million study at the behest of the Food and Drug Administration, which quickly said cellphones are safe.

“The current safety limits for cellphones are acceptable for protecting the public health,” FDA radiation health chief Dr. Jeffrey Shuren said in a statement. “Even with frequent daily use by the vast majority of adults, we have not seen an increase in events like brain tumors.”

Bucher said the typical cellphone use is “very, very, very much lower than what we studied.”

Rats and mice were bombarded for nine hours a day for up to years with a level so high that humans would only experience it briefly, if they have a weak cell signal, Bucher said in a news conference.

The toxicology program released preliminary results two years ago and finalized them Friday. The earlier report showed a hint of increased brain tumors in male rats, but the final results did not bear that out.

Bucher said the odd finding of the radiated rats surviving longer could be just chance or it could be that the radiation reduced inflammation in the rats, which in turn decreased the risk of a rat disease.

In 2011, a working group of the International Agency for Research on Cancer said cellphones are possibly carcinogenic. But numerous studies over the years, before and after that listing, have found little evidence of a problem.

Among the largest studies, a 2010 analysis in 13 countries found little or no risk of brain tumors, with a possible link in the heaviest users that the study’s authors found inconclusive. And a large Danish study that linked phone bills to a cancer registry found no risk even from more than 13 years of cellphone use, according to the latest update in 2007.

In December, the state of California put out a guide on how people could reduce exposure to radiofrequency from cellphones. It said “although the science is still evolving, some laboratory experiments and human health studies have suggested the possibility that long-term, high use of cellphones may be linked to certain types of cancer and other health effects.”