Just 10 minutes of chatting on cellular phones is enough to trigger such chemical changes in the brain that can increase the risk of cancer, warn scientists.

A study by the Weizmann Institute of Science in Israel has shown that even low levels of radiation from handsets interfere with the process of cell division, which encourages the growth of tumors.

Although the researchers have yet not found any evidence that signals from cell phones are harmful, their findings suggest they may be.

Several studies have been conducted to find an association between mobile use and brain tumours, but they neither found any such link nor any dramatic rise in cancer rates.

Ever since the inception of mobile phones, the official advice has been that the device are safe. The guidance is based on the assumption that the phones emit too little radiation to heat the brain dangerously.

The new study, however, suggests that "nonthermal" radiation can pose a risk.

In lab tests, the researchers exposed human and rat cells to low-level radiation at 875 megahertz, a similar frequency to the one used in many mobile phones.

Despite being weaker than emissions from a typical handset, the radiation began to switch on a chemical signal inside the cells within ten minutes, say the researchers. The chemical signals detected were involved in the division of cells, they add.

The researchers also claimed to have found a separate way in which mobile phones can damage health.

"The significance lies in showing cells do react to cellphone radiation in a non-thermal way," the Daily Mail quoted Dr Rony Seger, a co-author of the study published in the Biochemical Journal, as telling New Scientist magazine.