Mobile phone users may be at increased risk from brain cancer and should use texting and free-hands devices to reduce exposure, the World Health Organisation's cancer experts have said.

Radio-frequency electromagnetic fields generated by such devices are "possibly carcinogenic to humans," the International Agency for Research on Cancer (IARC) announced at the end of an eight-day meeting on Tuesday in Lyon, France. Experts "reached this classification based on review of the human evidence coming from epidemiological studies" pointing to an increased incidence of glioma, a malignant type of brain cancer, said Jonathan Samet, president of the work group.

Two studies in particular, the largest conducted over the last decade, showed a higher risk "in those that had the most intensive use of such phones," he said in a telephone news conference. Some individuals tracked in the studies had used their phones for an average of 30 minutes per day over a period of 10 years. "We simply don't know what might happen as people use their phones over longer time periods, possibly over a lifetime," Samet said.

There are about five billion mobile phones registered in the world. The number of phones and the average time spent using them have both climbed steadily in recent years.

The IARC cautioned that current 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 non-malignant tumour 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.