The World Health Organization said the use of cell phones and other wireless devices may be "carcinogenic to humans."
Two large studies link cell phone use with higher rates of glioma, a type of cancer.
Using cell phones for calls is considered more risky than using them for texting.
The use of cell phones and other wireless communication devices are "possibly carcinogenic to humans," the World Health Organization's cancer research agency said Tuesday.
The radio frequency electromagnetic fields generated by such devices were deemed as potential cancer agents "based on an increased risk for glioma, a malignant type of brain cancer," the International Agency for Research on Cancer (IARC) said in a statement.
A group of experts meeting in the French city of Lyon over the past eight days "reached this classification based on its review of the human evidence coming from epidemiological studies," said Jonathan Samet, president of the work group.
Two studies in particular, the largest conducted over the last decade, provided evidence that cell phone use was associated with higher rates of glioma, "particularly in those that had the most intensive use of such phones," Samet said.
A number of individuals tracked in the studies had used their phones for 10 to 15 years.
"We simply don't know what might happen as people use their phones over longer time periods, possible over a lifetime," he said.
There are about five billion mobile phones registered in the world.
Both the number of phones in circulation, and the average time spent using them, have climbed steadily in recent years, the working group found.
The IARC cautioned that their review of scientific evidence showed only a possible link, not a proven one, between wireless devices and cancers.
"There is some evidence of increased risk of glioma" and another form of brain cancer called acoustic neuroma, said Kurt Straif, the scientist in charge of editing the IARC reports on potentially carcinogenic agents.
"But it is not at the moment clearly established that the use of mobile phones does in fact cause cancer in humans," he said in a telephone press conference.
The IARC does not issue formal recommendations, but pointed to a number of ways consumers can reduce risk.
"What probably entails some of the highest exposure is using your mobile for voice calls," Straif said.
"If you use it for texting, or as a hands-free set for voice calls, this is clearly lowering the exposure by at least an order of magnitude," or by ten fold, he said.
A year ago the IARC concluded in a major report that there was no link between cell phones and brain cancer, but the review was widely criticised as based on out-of-date data that did not correspond to current usage levels.
The new review, conducted by a panel of 31 scientists from 14 countries, was based on a "full consensus," said Robert Baan, in charge of the written report, yet to be released.
Exposure data, studies of cancer in humans, experiments on animals and other data were all evaluated in establishing the new classification.
The IARC ranks potentially cancer-causing elements as either carcinogenic, probably carcinogenic, possibly carcinogenic or "probably not carcinogenic." It can also determine that a material is "not classifiable."
Cigarettes and sunbeds, for examples, are rated as "group 1," the top threat category.