Radiation from mobile phones may affect the brain development of unborn babies, the lead author of a controversial animal study has claimed.
Pregnant mice placed in the vicinity of an active mobile phone gave birth to offspring which showed signs of hyperactivity, anxiety and poor memory.
Infant mice whose mothers were not exposed to the radiation were not affected the same way.
The changes were attributed to impaired development of neurons in the prefrontal cortex of the brain.
According to the US scientist who led the research, the same effects could potentially occur in humans.
Professor Hugh Taylor, from Yale University, believes mobile phones might even be partly responsible for rising rates of behavioural disorders such as attention deficit hyperactivity disorder.
However, other experts warned strongly against extrapolating the findings and assuming they were relevant to humans. One called the claims ''alarmist and unjustified''.
The research is reported in the Nature publication Scientific Reports.
Prof Taylor said: ''This is the first experimental evidence that fetal exposure to radiofrequency radiation from cellular telephones does in fact affect adult behaviour.
''We have shown that behavioural problems in mice that resemble ADHD (attention deficit hyperactivity disorder) are caused by cell phone exposure in the womb.
''The rise in behavioural disorders in human children may be in part due to fetal cellular telephone irradiation exposure.''
He added that more work was needed in humans to investigate the mechanisms involved and establish safe levels of mobile phone exposure during pregnancy.
ADHD is a development disorder characterised by inattention, hyperactivity and impulsiveness.
Between 3% and 7% of school-age children suffer from the disorder. Affected children tend to perform poorly at school and are at increased risk of delinquency.
Diagnosis of ADHD has increased at an average rate of 3% per year since 1997, making the condition ''a growing public concern,'' according to the scientists.
In the study, 33 pregnant mice were exposed to radiation from a muted but active mobile phone positioned a short distance above their cage. The phone was placed on an uninterrupted call for 17 days, almost the whole of their pregnancy.
A comparison group of pregnant mice was kept under the same conditions but with the mobile phone switched off.
More than 160 adult offspring were were given a series of psychological and behavioural tests and had measurements taken of their brain electrical activity.
Co-author Tamir Aldad, also from Yale, pointed out that rodent pregnancies last only 19 days and mice are born with a less developed brain than humans.
Further research was needed to determine whether the potential risks of exposure to mobile phone radiation in pregnancy were similar for humans.
''Cell phones were used in this study to mimic potential human exposure but future research will instead use standard electromagnetic field generators to more precisely define the level of exposure,'' said Dr Aldad.
Other experts also urged caution.
Professor Eric Taylor, a child psychiatrist from the Institute of Psychiatry at King's College London, said: ''This paper does not show any link between radiofrequency exposure and ADHD. The rate of ADHD problems has been steady for more than 20 years (any increase is due to greater recognition), so mobile phones are an unlikely cause.
''Taking animal studies and extrapolating directly to humans requires much more care. The exposure of the animals was very great, and the researchers' tests of animal memory should not be directly equated to human attention; different species can react differently.''
Professor Katya Rubia, a neuroscientist also from the Institute of Psychiatry, said: ''The extrapolation of the behavioural and brain effects of prenatal mobile phone exposure in mice to human ADHD and its increase in our society is alarmist and unjustified.
''Some enhancement in motor activity in mice is not translatable to the complex human ADHD behaviour characterised by impulsiveness, inattention and motor activity. ADHD is not associated with memory problems, or with decreased anxiety, and the key brain deficits are in the basal ganglia rather than the frontal lobe.''
Dr Mischa de Rover, a psychologist at Leiden University in the Netherlands, said: ''Good animal data is of crucial importance as a starting point for human studies but should never be used as a basis for risk assessment in humans.''