No arrests had been made and the motive behind the crime was unclear. PHOTO: FILE
The incident took place in the Shamli district of Uttar Pradesh, about 100 kilometres from the capital, on Tuesday evening when the sisters, three of whom are teachers, were returning home from a government school.
"The victims were walking together when two men on a motorbike made lewd remarks and the man who was riding pillion splashed acid on all of them," Abdul Hammed, senior police officer who is investigating the case told AFP.
Hameed said no arrests had been made and the motive behind the crime was unclear.
"The youngest sister suffered maximum burn injuries and she had to be rushed to a hospital in Delhi."
Attacks on women have topped the national agenda since December 2012 when a medical student was assaulted and raped by six men on a moving bus in Delhi. She died two weeks later of her injuries.
Public anger prompted parliament to toughen sex offence laws including doubling the minimum prison sentence for gang-rape to 20 years, but lawmakers voted against making acid attacks punishable with life imprisonment.
Acid attackers can be jailed for 8-12 years depending on the injuries inflicted, but the offence is bailable.
Activists have asked that India should regulate the sale of an acid called "Tezaab" which is designed to clean rusted tools but is commonly used in attacks.
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