The incident came to light when the sisters, who had gone missing while on a visit to Delhi, returned today and narrated the incident to their family.
According to a complaint filed by the victims' father, the girls were abducted by one Nafis and three others and gangraped, said SHO Indirapuram Hardayal Yadav.
The girls, residents of Bharatnagar here, have been sent for medical examination, he said, adding that a manhunt is on to nab the accused.