The body of the minor, who went missing Monday morning, was found surrounded by stray dogs, police said.
Her mother alleged that she was abducted, raped and later murdered, they said.
Post mortem report of the girl revealed that she had over 50 stab wounds and severe internal injuries, sources said.
IG (law and order) R K Vishwakarma said that an FIR has been registered under Sections 302 (murder) and 376 (rape) of the IPC against unidentified persons.
Regarding allegation that local police tried to hush up the matter, the IG said that SSP Lucknow has been asked to conduct an inquiry.
Samples from the body of the girl have been sent to forensic laboratory for further examination.