NEW DELHI (AFP) - India's top court on Monday ordered a judge to release his 30-year-old daughter who was being detained because he disapproved of her marrying her boyfriend from a different caste.

The Supreme Court ordered Ms Supriya Rathore be reunited with her boyfriend who was forced to take legal action to have her released from her father, a high court judge in the northwestern state of Rajasthan.

"She is a major and has the liberty to make her choice in marriage," judges H.L. Dattu and C. Nagappan told the couple, who were in the court in New Delhi for the ruling.

The boyfriend, Mr Siddharath Mukherjee, had petitioned the court, saying the father, who belongs to the Hindu Rajput warrior caste, opposed his daughter marrying a man from the Bengali-speaking Brahmin caste.

Ms Rathore herself had also e-mailed police and the courts during her month-long detention at the family home in Jaipur city, seeking their help to get her released and reunited.

Acting on the boyfriend's petition, the court ordered police on Dec 12 to transport Ms Supriya to New Delhi for Monday's hearing.

"I have no complaints against anyone including my parents," Ms Supriya told the court during the hearing.

"I love them all but I want to go with Siddharath Mukherjee as I want to marry him," she said, as the court offered her protection if she felt threatened in any way.

India has officially banned its hereditary caste hierarchy but the rigid system still exists. Young couples are targeted by their families, clans or communities who disapprove of relationships outside of their own castes.

So called honour killings also still occur in India, which usually result from disputed inter-caste relationships that see male family members murder their daughter or sister for bringing "dishonour" on the family.

The ruling comes as India marks 12 months since the fatal gang rape of a 23-year-old student on a Delhi bus, a horrific crime which sparked soul searching about the way women in patriarchal India are treated.