Kumamoto City, Japan - Around 100 dead cats were discovered at the squalid home of a woman in southwest Japan who was a member of an animal welfare group, a local official said on Wednesday.

The group, Animal Assist Senju, apologized on social media, posting pictures of the trash-strewn house it said "was overflowing with feces and urine".

The residence belonged to one of its staffers, who the group said was found to have gone rogue and taken in many cats without consulting the organization.

One cat was found "unrecognizable" with "its skin partly peeled off and paws covered in feces and urine", the group said in an Instagram post over the weekend.

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Kumamoto City's animal protection center told AFP on Wednesday that the dead felines were initially estimated to total "around 100".

Media reports however said the number is now thought to be higher.

Animal Assist Senju, based in the region of Kumamoto, says it rescues cats and dogs from animal shelters and transfers them to new homes.

"All the members of our group take what happened very seriously," it said in another Instagram post.

"We can only imagine what agonizing pain the cats went through before dying."

The woman is no longer allowed to take in cats, it said.

City officials and animal rights volunteers inspected the house twice after they were notified last week of a feline death, before launching a full search and rescue mission.

It is not clear if legal action has been taken against the woman.

Twelve live cats have been saved from the home so far, according to city animal protection official Tsutomu Takimoto.