All of the male pupils and staff at a private French Catholic school are to be swabbed by police after a 16-year-old girl was raped in the school toilets.

The 475 pupils, 31 members of staff and 21 other employees of Fenelon Notre-Dame school in La Rochelle will all be required to have DNA samples taken.

The victim said she was unable to identify the rapist, who attacked her from behind after the automatic toilet light went off on 30 September last year. A DNA sample was found on her clothing, but it does not match that of any of her family or friends, said prosecutor Isabelle Pagenelle.

The DNA will be collected over three days by 18 police officers from Monday by taking saliva from inside the cheeks and under the tongue, said Pagenelle.

The school's headteacher Chantal Devaux said: "We have followed every lead before going down this route. We don't have any other choice."

A psychological support unit has been set up to help the school's 1,300 pupils.

Pagenelle said there was a significant possibility the attacker was from the school, and that police had a list of everyone who was on the school premises at the time of the rape.

Testing minors will require parental approval, and the swabs of those ruled out will be destroyed.

Police said that those who refuse to take the test will be treated as suspects.

The result of the tests will be known in a month, said Pagenelle.