The RSPCA is investigating a report that an eight-year-old boy put his neighbour's cat into a microwave oven.
The caller claimed the pet's owner came downstairs after hearing the microwave being operated and found that his neighbour's young son had put the animal inside, said a spokeswoman for the charity.
The incident is alleged to have taken place in Rochester, Kent, and was reported to the RSPCA on Saturday.
But because the accused child is under the age of 10, the RSPCA and the police cannot start criminal proceedings against him.
RSPCA Inspector Ray Bailey said he had contacted the youth offending team at Medway police station regarding the incident.
The cat was taken by its owners to the PDSA charity for treatment and is recovering, said the RSPCA spokeswoman.
But she added that damage caused by the microwave could have permanently harmed internal organs so the cat may have ongoing problems.
Mr Bailey said: "This was an absolutely horrendous incident and all the more shocking because of the alleged involvement of such a young child."
The RSPCA has prosecuted 82 people aged 17 and under over the past three years for offences including kicking a hedgehog to death, kicking guinea pigs to death and stealing a pet chicken before torturing her and ripping her head off, said the spokeswoman.
The charity said it is pushing for tougher penalties for those who commit the most serious of crimes against animals.