A study into the safety of mobile phones has found no evidence to support claims of links with cancer.

The industry-funded research found no increase in any type of tumour in rats exposed to mobile phone radiation.

It comes a week after a major Finnish study suggested radiation from mobile phones caused changes in the brain.

The latest study on rats was carried out by scientists in the United States.

We tried to mimic a high level of exposure that humans might experience

Professor Joseph Roti Roti

It was financed by Motorola Inc and the US research organisation, Integrated Laboratory Systems.

In experiments, rodents were given doses of radiation designed to mimic levels humans might receive when using mobile phones frequently.

The rats were then exposed to the two most common types of cell phone radiation for four hours a day, five days a week, for two years.

Researchers at the Washington University School of Medicine in St Louis looked for signs of cancer in brain cells and nearly 30 other tissues.

"We tried to mimic a high level of exposure that humans might experience," said Joseph Roti Roti, professor of radiation oncology at the university.

"We found no statistically significant increases in any tumour type, including brain, liver, lung or kidney, compared to the control group."

Twists and turns

The evidence is the latest in a series of often contradictory studies into the safety of mobile phones.

The Finnish research was the first to look at the effects of mobile phone radiation on human cells rather than those of rats.

Experts from Finland's Radiation and Nuclear Safety Authority found that exposing human cells to mobile phone radiation damaged the blood-brain barrier.

This is a natural barrier that stops harmful substances in blood from entering the brain.

Both the Finnish and US research will be presented at a scientific meeting in Quebec City, Quebec, this week.

Hands free

Dr Michael Clark, science spokesman for the UK's National Radiological Protection Board, said the latest work on rats confirmed earlier findings.

He told BBC News Online: "This work shows no effect of radio-frequencies and that's what we would expect.

"Similar work was done in the 70s and 80s in animals and showed no effects."

Professor Roti Roti believes the greatest safety risk from mobile phones is when driving.

"As far as I can tell from the work so far the greatest hazard with cell-phones is driving a car while talking on one," he said.

In the UK, the Faculty of Public Medicine will call this week for employers in the public sector to ban staff from using mobile phones - even on hands free - while driving.

Vice-president Dr Peter Donnelly says drivers should refuse to use their phones while on the road and employers should not expect them to receive calls.