Governor Carepa said she was shocked at the reports

The governor of the state of Para, where the reported case took place, has promised a full inquiry.

Governor Ana Julia Carepa said the age of the woman, put variously at 15 and 20, was irrelevant as she should not have been jailed with male prisoners.

Women's rights groups in Brazil say it is not an isolated case.

According to reports in the Brazilian media, the number of men in the cell with the young woman ranged between 20 and more than 30.

Public anger

Media reports suggested that the girl was placed in a police cell in the town of Abaetetuba on suspicion of theft.

But human-rights groups say there is uncertainty about what offence the girl was accused of and she was not formally charged.

Whether she was 15, 20, or 100 doesn't matter. A woman should never be left in a jail with men

Governor Ana Julia Carepa

Brazil's notorious prisons

The girl's father has now alleged that he has been threatened by police who tried to force him to provide a birth certificate showing that the girl was 20 years of age - a document which he said did not exist.

The police are said to have believed at one stage that the girl was not under age.

Public anger

Gov Carepa said the girl's age did not matter.

"Whether she was 15, 20, or 100 doesn't matter. A woman should never be left in a jail with men," she said.

Jails in Brazil are notorious for overcrowding and appalling conditions, and this is not the first time that there has been a controversy over a female prisoner being detained alongside men.

However, on this occasion, the seriousness of the allegation has caused shock and considerable public anger, the BBC's Gary Duffy in Sao Paulo says.

Women's rights groups in Para state quoted by the Globo website say there have been at least three cases of women being put in cells with men.