A ruling by Italy's highest appeals court that said those charged with gang rape do not always have to go to prison while awaiting trial has outraged women's groups and some politicians who fear it will make rape a third-class crime.

The court, ruling on a point of law in the appeal of two 19-year-old men charged with gang raping a 13-year-old girl, said Thursday that judges could decide on a case-by-case basis whether to prescribe jail, house arrest or other forms of detention such as checking in with police once a day while they were awaiting trial.

Pre-trial custody was previously obligatory for those charged with gang rape while house arrest was permissible in some cases of those charged with rape committed by an individual, particularly a minor.

Critics fear the ruling could encourage some judges to mete out lenient sentences in future gang rape cases.

This is a ruling that risks making gang rape a third-class crime, said Giulia Bongiorno, one of Italy's most famous criminal lawyers.

Given that rape is already an abominable crime, gang rape is even worse - if that is possible. But there is a cultural problem in Italy. Many people consider theft or purse-snatching crimes worse than rape, she said.

Alessandra Mussolini, the granddaughter of Italy's wartime fascist dictator and now a right-wing parliamentarian, called the ruling abhorrent and said it was a time bomb waiting to go off that could risk increasing the rate of rape.

A woman who sees her torturer spared from prison is raped twice, Mussolini said.

According to national statistics institute ISTAT, there were 200 rapes or attempted rapes in Italy every day in 2006, the latest year for which full statistics are available.

At the time of that study, some 1 million Italian women between the ages of 16 and 70 said they had been raped.

At a time when sexual violence against women is the subject of so many legislative initiatives, I ask myself how such a ruling is possible, said Barbara Saltamartini, a center-right parliamentarian.

She said the court ruling had prompted the utmost contempt and sadness in me and had undermined efforts to combat rape, particularly on the cultural level.

Talking about rape is still a cultural taboo in many parts of Italy, particularly the poorer south, where shame over being a victim of the crime is embedded in traditional societies.

According to some estimates, only 5 percent of rape victims in Italy report the crime to police.

(Reporting By Philip Pullella; Editing by Barry Moody and Alison Williams)