The largest-ever study into the possible health risks of using a mobile phone has proved inconclusive.

The World Health Organisation said that in most cases, phone users did not increase their risk of brain tumours.

There were "suggestions of higher risk" - 40 per cent higher for some tumours - for those who spoke on their phones for an average of half an hour a day on the same side of their head over a 10-year period.

But the researchers said "biases and errors" prevented them from making a causal link between mobile phones and tumours.

Al Jazeera's Nadim Baba reports. (May 18, 2010)