The Taleban made her brother hold her down, witnesses said
Pakistan's newly reinstated chief justice has ordered a police committee to investigate the controversial flogging of a teenage girl.
A video has been circulating of the public flogging in the north-western Swat valley which has sparked outrage.
Chief Justice Iftikhar Chaudhry said the probe should determine the victim and the perpetrators.
The film shows apparent Taleban members holding the girl down and hitting her with a strap as she cries out in pain.
Prime Minister Yusuf Raza Gilani has condemned the incident as "shameful".
The BBC's Barbara Plett in Islamabad says that the video has strengthened fears that the provincial government has capitulated to militants in Swat by agreeing to implement Islamic Sharia law there.
Justice Chaudhry had summoned police and officials from North West Frontier Province to the Supreme Court.
He has called the flogging a "cruel violation of fundamental rights".
Justice Chaudhry demanded regular updates on the progress of the police investigation.
The flogging has been condemned by many in Pakistan
He and other judges on the bench strongly criticised the summoned officials.
The judges said the government had failed to establish its authority in Swat, despite a peace deal there.
Citing recent attacks, they also warned that the menace of militancy was spreading to Islamabad.
The video has triggered protests by women's and civil society activists against the growing strength of Taleban influence.
Local sources said the girl in the video had been accused of illicit relations with a man and that the flogging took place about a month and a half ago.
Local officials say it took place before the peace deal with militants, which includes the implementation of Sharia law, was signed.
The burka-clad 17-year-old is heard crying throughout the two-minute flogging and at one point swears on her father that she will not do it again.
Relatives of the man involved in the incident told the BBC he had gone to the house of the girl in the village of Kala Kalay to do repairs as an electrician, but militants accused him of having a relationship with her.
They dragged him from the house and flogged him before punishing the girl, his relatives said.
The Taleban made the girl's brother hold her down during the flogging, they said.
After the incident, the Taleban forced the couple to marry and instructed the man not to divorce his wife. His relatives say he has been left mentally scarred.
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