The 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 yesterday in Lyon, France.
A group of 31 experts from 14 countries has "reached this classification based on its review of the human evidence coming from epidemiological studies", ABC News reported.
The experts also pointed to an increased incidence of glioma, a malignant type of brain cancer, International Agency for Research on Cancer (IARC) said in a statement.
The number of mobile phone subscriptions is estimated at 5 billion globally.
"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," said Jonathan Samet from the University of Southern California, the Chairman of the group of scientists.
The IARC, which is part of the WHO, cautioned that current scientific evidence showed only a possible link, not a proven one, between wireless devices and cancers.
"It is important that additional research be conducted into the long-term, heavy use of mobile phones," Christopher Wild, director of the IARC said.
"Pending the availability of such information, it is important to take pragmatic measures to reduce exposure such as hands-free devices or texting."