A landmark $30 million study by the World Health Organization shows the long term use of cell phones may be linked to cancer.

Researchers found a "significantly increased risk" of some brain tumors related to using mobile phones for ten or more years.

Health officials have concluded that precautions are important, according to the London Telegraph.

"In the absence of definitive results and in the light of a number of studies which, though limited, suggest a possible effect of radio frequency radiation, precautions are important," the study's lead researcher, Dr. Elisabeth Cardis, said.

Some suggest that children should be discouraged from making non-essential calls and that adults should keep calls short.

The study covered 13 countries and interviewed those with tumors as well as healthy cell phone users. Researchers interviewed 12,800 people.

The results are expected to be published by the end of the year.