A cat's head was found "deliberately" placed in a children's playground.
A staff member at Homerton Grove Adventure Playground made the grim discovery as she was opening the park in Wardle Street, Hackney, on Monday, April 24.
The head had apparently been placed beneath a piece of climbing equipment.
Michael Harrington, an RSPCA animal rescue officer, said: "This is a truly horrifying story.
"We were alerted to the discovery of a dismembered black and white cat head at a children’s playground on Monday last week (April 24)."
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The investigation is ongoing, but the RSPCA believes it was a deliberate act.
Mr Harrington continued: "The head was very carefully placed at the bottom of a children’s play apparatus and left in a way that it would be easily found.
"We have been informed that this particular piece of apparatus is one of the most used and popular things in the playground.
"This must have been a shocking discovery for the member of staff who stumbled upon it, but we are profoundly grateful that it was not found by a small child who could have been deeply traumatised."
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The head was found near the park's main entrance in Wardle Street.
The RSPCA believe the incident took place between 6pm on April 23 and 3.30pm on April 24.
Mr Harrington added: "This is a completely unthinkable act and we very much hope someone will have seen or heard something that can help us with our investigation.
"It is a uniquely disturbing situation and we are keen to get to the bottom of what happened here."
The organisation has been unable to obtain CCTV footage from the scene so is appealing to the public for information.
Anyone with information that could help is asked to call the RSPCA appeals line in confidence on 0300 123 8018.
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