French police are questioning three schoolgirls in a Paris suburb suspected of torturing a younger girl, in a bullying ordeal that lasted months.

The victim's father told Europe 1 radio the attackers had stubbed out cigarettes on the 12-year-old's face and arms, dislocated her jaw, slashed her with a knife and urinated on her.

The gang in Creteil extorted money from her and tortured her after she had gone to steal from a grocer's, it is alleged.

Police were alerted after that attack.

The three schoolgirls detained by police are aged 13 to 15.

In the radio interview, the girl's father said: "It's very complicated - she kept silent about it, and finally she told us 'I feared causing problems for you'."

After the attack the girl herself - given the name Sandra in French media - spoke about the bullying ordeal.

The girl's mother, quoted by the daily Le Parisien, said that on Tuesday she had found her daughter bloody and shaken in the street, and "discovered what they had subjected her to since December".

"We had noticed that money and jewellery had gone missing at home," she said. "Now we've got to leave this area... There's no way we can continue living in Creteil."

The victim attended the Clement Guyard school in Creteil, where a spokeswoman for parents said: "We're all shocked by this - we weren't aware of any particular problems. This must have gone on outside the school.