NEW DELHI: The father of an Indian schoolgirl who died after being pushed from a bus while resisting an alleged sex attack refused Saturday to release her body for postmortem until a powerful politician is arrested for her death.

The 16-year-old, who was travelling with her mother in a bus owned by the ruling family of northern Punjab state, died on Wednesday while resisting an alleged assault before being thrown out of the moving bus.

“Until police book Sukhbir Badal for my daughter's death, we will not allow her postmortem or cremate her,” Sukhdev Singh, the girl's father, told AFP.

Singh alleged he is being pressured to accept compensation money of two million rupees (around $30,000) as his wife, who was seriously injured in the attack, is recuperating at a hospital in Moga district.

Police said the chartered bus belongs to a company owned by Punjab deputy chief minister Sukhbir Badal but they do not have any legal grounds to file a case against him.

“We are investigating the case. There has to be some legal grounds to charge a person for a crime,” Moga police chief Jatinder Singh Khehra told AFP.

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The police chief said a postmortem was critical in criminal cases and the refusal to allow one could jeopardise the case in a court of law.

Police have arrested four suspects over the attack, including the bus conductor and a cleaner.

The attack has sparked heavy criticism from opposition parties on the state government, which is headed by Sukhbir's father Prakash Singh Badal.

The junior Badal has rejected the allegations and vowed to punish the guilty.

“It is absurd even to think that the company's ownership will allow such brutality and brazenness to go unpunished,” he told reporters.

The attack carries echoes of an infamous gang-rape and murder in New Delhi in December 2012 when a physiotherapy student was thrown off a moving bus, dying of her injuries a fortnight later.