They say that gangs of young thieves, some as young as 12, are increasingly attacking single women and lone teenagers in shopping areas in the centre of both towns. Tram stops and the railway station are also being targeted.
â€˜These groups are very intimidating and if the victim does not hand over their phone or tablet they do not hesitate to use violence and to hit out if they try to resist,â€™ said a police spokesman in Le Havre where the force has launched a â€˜warâ€™ against this kind of crime.
Police patrols in the city are being increased and detective work is underway to try to identify the thieves and information is being centralised in an attempt to find out more about the gangs.
Commissioner Patrick Longuet, head of urban security with the Le Havre police, said that the goal is to build up profiles of those responsible. A specialist group of eight police has been set up to investigate with four of them giving priority to the theft of mobile devices.
Recently 12 people were detained in Le Havre in the space of 15 days. â€˜We are getting four to five complaints a day,â€™ explained Longuet, adding that there has also been an increase in the number of people falsely claiming to be the victim of phone theft and this is not helping the investigations.
He pledged to crack down on this kind of behaviour as well. A young girl was recently fined â‚¬250 for falsely claiming her phone had been stolen.
In Rouen the attacks are happening most frequently in metro stations. Last month one young thief ran into one of the tunnels when he was confronted and the whole system had to be shut down while he was apprehended.
â€˜We are faced with real predators that choose their victims according to two criteria; they are vulnerable and they are carrying a state of the art device. These thieves act very quickly and can be violent if the victim resists. The best thing to do is not to resist,â€™ said Longuet.
Police are also advising the owners of the top of the range devices such as ipads and smart phones to use technology to render them unusable by thieves. The French Ministry of the Interior, for example, has a website where mobile telephones can be registered and a message is sent to the telephone operator if it is stolen.