Radiation from cell phones could possibly cause cancer, according to the World Health Organization.

In a report issued today, the International Agency for Research on Cancer (IARC), which is an arm of the WHO, said it now lists mobile phone use in the same category as lead, gasoline engine exhaust, and chloroform. Officially, cell phone radiation is listed as a "carcinogenic hazard."

Until today, the WHO's IARC had said that there were no adverse health effects from the use of cell phones. The wireless industry, including the CTIA lobbying group, and the Federal Communications Commission and U.S. Food and Drug Administration have also long maintained that cell phones are safe.

The CTIA, the wireless industry trade association in the U.S., was quick to point out that the WHO's IARC did not say that cell phones definitely cause cancer.

"IARC conducts numerous reviews and in the past has given the same score to, for example, pickled vegetables and coffee," John Walls, vice president of public affairs for CTIA, said in a statement. "This IARC classification does not mean cell phones cause cancer. Under IARC rules, limited evidence from statistical studies can be found even though bias and other data flaws may be the basis for the results."

The group also emphasized that the IARC's determination was based on reviewed published studies and was not the result of new scientific research.

"The IARC working group did not conduct any new research, but rather reviewed published studies," Walls continued. "Based on previous assessments of the scientific evidence, the Federal Communications Commission has concluded that '[t]here's no scientific evidence that proves that wireless phone usage can lead to cancer.' The Food and Drug Administration has also stated that '[t]he weight of scientific evidence has not linked cell phones with any health problems.'"

In response to Tuesday's news, an FCC spokesman said, "The FCC currently requires cell phones to meet safety standards based on the advice of federal health and safety agencies. We support the IARC recommendation for more research to clearly identify any potential health risks and, as appropriate, consider whether further actions may be required."

The new determination from the WHO's IARC was established at a meeting in France where a team of 31 scientists from 14 countries, including the United States, considered peer-reviewed studies about the safety of cell phones. The team said that it had found enough evidence to consider exposure to cell phone radiation as "possibly carcinogenic to humans."

The scientists reiterated what many in the field have said for years, which is that there are not enough long-term studies to decisively say one way or another whether cell phone radiation causes cancer. But there is enough data to show connections between exposure and health risks for consumers to be concerned.

Jonathan Samet, a medical doctor and professor from the University of Southern California, and the overall Chairman of the IARC's Working Group, which reviewed the studies, said in a statement today that "the evidence, while still accumulating, is strong enough to support a conclusion and the 2B classification. The conclusion means that there could be some risk, and therefore we need to keep a close watch for a link between cell phones and cancer risk."

The IARC has not yet published new guidelines for cell phone use, but the director of the organization suggested that concerned consumers take precautions to reduce exposure. He also emphasized the need for more research.

"Given the potential consequences for public health of this classification and findings, it is important that additional research be conducted into the long-term, heavy use of mobile phones," IARC Director Christopher Wild said in a statement. "Pending the availability of such information, it is important to take pragmatic measures to reduce exposure such as handsfree devices or texting."

The IARC said in a statement that it considered hundreds of scientific articles, including some recent articles that had been published as a result of the 10-year Interphone study.

A report summarizing the main conclusions of the IARC Working Group and the evaluations of the carcinogenic hazard from radiofrequency electromagnetic fields, including the use of cell phones, will be published in the medical journal, The Lancet Oncology in its July 1 issue. The IARC also expects to publish the full report online in a few days.

A year ago, the IARC published some results from the Interphone research project, an ambitious, decade-long study that included data gathered by 21 scientists from around the world to study 13,000 individuals in 13 different countries. It was the largest research program to study the effects of cell phone radiation to date, but many researchers conceded that the results of the study were inconclusive.

Initially, the official word from the WHO's IARC was that most cell phone use did not lead to an increased risk of either meningioma, a common but typically benign form of cancer, or glioma, a rare but more dangerous type of brain cancer. But the group conceded that more research is needed, especially since cell phone use has increased dramatically since 2000, particularly among younger people.

"An increased risk of brain cancer is not established from the data from Interphone," Wile, IARC's director, said in a statement at the time that the report was issued. "However, observations at the highest level of cumulative call time and the changing patterns of mobile phone use since the period studied by Interphone, particularly in young people, mean that further investigation of mobile phone use and brain cancer risk is merited."

Some experts have interpreted the results to suggest that people who use a cell phone for at least an hour each day over a 10-year period are at an increased risk of developing some brain tumors. This research, these experts argue, also suggests that these tumors are more likely to be on the side of the head where the phone is most often used.

However, the authors of the epidemiological studies that came to these conclusions have acknowledged that possible biases and errors from those participating in the survey meant that these results were not conclusive enough to directly blame cell phone radiation for such tumors. For example, critics of these studies say that subjects may have recall bias. Subjects in the study diagnosed with brain tumors may have better recall of how often they used their cell phones and on which side of their heads they usually placed their phones than the control groups that do not suffer from these ailments.

Today's determination by the WHO's IARC that cell phone use could cause cancer still does little to clear up the confusion around whether cell phones present a significant risk to human health. We simply still do not know. But to date, the World Health Organization's warning is the most significant one so far to suggest that people take precautions.

CNET has spent the past several months digging deeper into this issue. And in a three-part special report that began this morning, we take a look at the maddening state of cell phone safety research. The first part of the report was published today and takes a look at the confusing state of the scientific evidence. Later this week, CNET will explain how regulators came up with the safety standards and how they test devices. Finally, we will look at what consumers can do to protect themselves and discuss what some communities are doing to make sense of this mess. CNET has also published a Q&A with Devra Davis--an epidemiologist, author, and founder of the Environmental Health Trust--about her new book "Disconnect: The Truth about Cell Phone Radiation, What the Industry Has Done to Hide it and How to Protect Your Family.

Updated 12:50 p.m. PT: This story was updated with comments from the CTIA and more information from the IARC's report.

Updated 2:35 p.m. PT: Comments from an FCC spokesman were added to this story.