One of the world’s rarest species of bear has become even more endangered after park staff in Italy accidentally killed one of the animals.

Biologists in the National Park of Abruzzo, Lazio and Molise had captured the young male brown bear and had injected him with an anaesthetic when he started having difficulties breathing. He could not be saved.

WWF, the environmental organisation, called for procedures for catching and sedating bears to be immediately reviewed.

“We await the post-mortem results in order to clarify what happened, but this is without doubt a very serious loss,” said WWF Italia.

“This is a sub-species on the brink of extinction, reduced to a population of just 50 individuals.”

The Marsican bear, Ursus arctos marsicanus, lives in the Apennine mountains and forests of central Italy.

The park rangers had been reportedly trying to capture and fit a radio collar to a large male bear nicknamed Mario, which has been raiding bee hives – but they caught the wrong one.

Park chiefs are now investigating what went wrong after the anaesthetic was given.

Antonio Carrara, the head of the park, said his staff were shocked by the death.

“For us, the loss of a bear is really serious and we want to find out what happened,” he said.

The park said later a post-mortem examination had ruled out a direct link between the anaesthestic and the cause of death, “confirming the correctness and regularity of the procedures implemented by the park staff and the veterinarian in particular”.

It said: “The animal, therefore, had serious health problems, which cannot be assessed by the clinical examination at the time of capture, which determined the anaesthetic emergency and consequently the death of the animal.”

Laboratory tests should establish the cause of death, the park added.

It is the second time in four years that an Italian bear has died accidentally under sedation. In 2014, a bear named Daniza also died after being anesthetised.