The police are yet to identify the girl.
A minor was allegedly held captive, tortured and raped before being killed, the Surat Police said on Sunday weeks after the rape and murder of an eight-year-old girl in Kathua in Jammu region sent shock waves across the nation.
The body of the unidentified girl, believed be between nine and 11 years, was found in Bhestan locality in Surat and had 86 injury marks, they said.
It was spotted lying in bushes near a cricket ground on the morning of April 6 by some passersby, the police said.
The autopsy report said there were 86 injury marks on her body, including the private parts, indicating that she was tortured and raped, Inspector K B Jhala of Pandesara police station said. She was strangulated, the report said.
While the police had earlier said that a body of a girl had been found, details of the case were made public on Sunday with Surat Police Commissioner Satish Sharma holding a press conference.
An FIR has been lodged under sections 302 (murder), 323 (voluntarily causing hurt) and 376 (rape) of the IPC and under the Protection of Children from Sexual Offences Act against unidentified persons, he said.
Ganesh Govekar, a doctor at the City Civil Hospital where the autopsy was conducted, said, "Going by the nature of injuries, they seem to have been caused over a period ranging from one week to a day prior to the recovery of the body, suggesting that the girl, who is between nine to 11 years of age, might have been held captive, tortured and possibly raped."
The police commissioner said the investigation has been handed over to the city police's crime branch and all efforts are being made to identify the girl.
"We have gone through the data of missing children in Gujarat and also in other states like Odisha and West Bengal, as she might be from another state," he said.
"There was no sign of struggle at the spot where the body was found. The post-mortem report says she was killed six to 24 hours before the body was dumped. It is possible that she is from outside Surat," he said.
"We need to identify the girl to solve the case. We are focusing on Odisha and West Bengal, as she is likely to be from either of the two states," he said, adding that so far the police have scanned data of 8,000 missing children.
"We have taken a DNA sample for identification. We will also obtain a report from the forensic science laboratory as soon as possible," he said.
The police have announced a Rs 20,000 reward for anyone helping in identifying the girl or giving information about the culprits, Sharma said.