"We have arrested the mother of Zeenat and are looking for her brother for allegedly setting her on fire, killing her on the spot," Lahore police spokesman Nayyab Haider told PTI.
He said Zeenat's mother Parveen told the police in custody that her daughter had committed an 'unforgivable' crime by marrying a man after eloping with him.
"Although Pareveen confessed to her crime, she denied the involvement of her son in killing Zeenat," Haider said.
Zeenat reportedly fell in love with Hasan, who lived in her locality, and asked her parents to accept his marriage proposal.
However, her parents refused following which Zeenat eloped with Hasan and married him in court.
The police official further said Zeenat, a resident of thickly-populated factory area, had contacted her mother a few days ago seeking her forgiveness for marrying against the will of her family.
"Parveen told her that she and other family members had forgiven her and she should return to take the blessing of her family," he said.
Getting into the trap, Zeenat agreed to return.
"Today, when Zeenat reached her parents' house, first she was tortured by her mother and a brother and then they doused petrol on her setting her alight," he said.
Police have registered a murder case against Parveen, her son and two unidentified men.
The girl's body has been shifted to a mortuary for autopsy.
Punjab Chief Minister Shahbaz Sharif has taken strict notice of the incident and directed Lahore police chief Amin Wains to thoroughly investigate the matter and bring the perpetrators to justice.
Last week, police arrested five men including a suitor for torching a 19-year-old school teacher in Murree, some 35 kilometres from Islamabad, for refusing to marry him.
Similarly, last month, police arrested 13 members of a local tribal council including the parents of a teenage girl for strangulating her and later torching her body in Abbottabad for marrying a man of her choice.
According to Human Rights Commission of Pakistan, around 800 women were killed last year in Punjab in 'honour killings'.
The Punjab government has introduced more strict legislation for protection of women.
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