A 15-year-old Christian girl has been kidnapped and forced to convert to Islam before being married to her abductor in Pakistan, her family have said.

The girl, identified as Saima Bibi, was abucted by a group of Muslim men when she was alone in a village in the Kasur district of Pakistan, her brother Riaz Masih said. The family have lodged a case against the kidnappers with police in Kasur.

"We have been told that she has married after converting to Islam with a Muslim man Tanvir, her kidnapper." Masih  told ucanews.com. "My sister... is 15 years old. We have her birth certificate, which will be produced before the court."

The legal age for marriage in Pakistan is sixteen, however a police officer said that Saima had converted to Islam and that officials have documents proving the marriage.

"This is unacceptable, we totally condemn this," said Father Joseph Louis, the executive secretary of Caritas Pakistan. He described the situation as an attack on religious freedom, and demanded "that courts give justice to the affected family".

Saima and her alleged-husband will appear before a local court, "where the girl can testify whether she was kidnapped or willingly married the Muslim man," a police spokesperson said.

The Movement for Solidarity and Peace (MSP), a research, education and advocacy group, have said this particular case is representative of a trend in Pakistan, where around 700 non-Muslim girls are converted to Islam each year. The Karachi-based Aurat Foundation estimates that the figure is closer to 1,000.

The forced marriages usually follow a similar pattern, in which a young girl is abducted, converted to Islam and then married to the abductor or a third party. According to MSP, the family often file a complaint, but that is then countered by the abductor.

The victim remains in the custody of her abductor throughout the case, during which time she may be subjected to "sexual violence, rape, forced prostituion, human trafficking and sale, or other dometic abuse," MSP said.

Christian lawyer Sardar Mushtaq Gill, head of Legal Evangelical Association Development, who has experience with similar cases, said "the perpetrators often take a plea of marriage and conversion to Islam so that they can save themselves from criminal charges of rape and kidnapping."