GENEVA (AFP) - UN human rights chief Navi Pillay on Tuesday urged India to ensure that perpetrators of caste-based sexual attacks do not escape justice.

"Women from stigmatised castes suffer the double assault of caste-based and gender-based discrimination," Ms Pillay said on the sidelines of a session of the UN Human Rights Council. "And all too often abuses of their rights are committed with complete impunity," she said.

"Such impunity must end," said Ms Pillay, a South African with Indian roots.

India has been trying to overcome its reputation for violence against women, but public outrage was reignited by the deaths last month of two girls, aged 12 and 14, who were gang-raped and lynched in their impoverished village in the state of Uttar Pradesh.

The girls' families refused to cut their bodies down from a tree in protest at alleged police inaction, which they said was because they were from a lower caste.

Last week, a woman said she had been gang-raped by four officers at a police station in the same state, and police said they were also investigating the death of a nineteen-year-old found hanging from a tree.

"The victims of these crimes must receive justice, and societies, communities and officials must receive the clear message that discrimination and violence will no longer be tolerated," said Ms Pillay.

"States must take steps to prevent such violence and discrimination and protect the rights of vulnerable people and communities," she added.

India brought in tougher laws last year against sexual offenders after the fatal gang-rape of a student in New Delhi in December 2012, an attack that drew international condemnation of India's treatment of women.

But the legislation, which was also designed to educate and sensitise police on rape cases, has failed to stem the tide of violence.

"Violence against women of poorly regarded castes has very deep roots, which cannot be tackled without far-reaching efforts. Clearly laws are necessary, but they are not enough," said Ms Pillay.

"There must also be fundamental change within communities, to peel off, layer by layer, the mind-set that generates caste discrimination and bigotry," she said.

Ms Pillay noted that caste-based discrimination was a global problem, hitting communities not only in India but other parts of Asia, as well as Africa, the Middle East and Europe.Around 260 million people are affected, she said.