Police are investigating the death of a nativity donkey in Spain after it was “squashed” by an obese man who climbed into its pen.

The five-month-old animal, called Platero, was not meant to be ridden as part of the Christmas scene in the town of Lucena, in Andalusia.

But according to a complaint by animal welfare groups, a 23 stone man climbed on the donkey’s back to pose for a picture that has caused outrage on social media.

Two days after the incident on 10 December, locals noticed the small animal could barely stand and it died the next morning after vets said they could not heal its injuries.

Activists likened the animal’s wounds to being “burst inside” and said it spent three days “in agony”, calling for the use of live animals in nativity scenes to be banned.

The Asociación de Defensa del Borrico (Association for the Defence of Donkeys) and the Círculo Animalista de Podemos Lucena (Lucena Animal Circle) have made a formal complaint to the police, who are now investigating.

A statement on Facebook said: “The nativity scene became a slaughterhouse…our Platero was literally squashed by a man whose photo was spread by WhatsApp users calling it a 'hazaña' (great achievement).

“The man climbed the fence and pushed Platero around until he could proudly pose “galloping” with almost 150kg of weight on his fragile body…fatally injuring him.”

The groups vowed to “move heaven and earth” to find out who was responsible, saying the incident was causing “outrage and repulsion” across Spain.

If a vet rules that the man caused the donkey’s death, the council may take legal action, El Mundo reported.