One of three lynx cubs born in captivity in Spain in March has died after a fight with one of its siblings.
Brezina (left) died after fighting with her brother Brezo (centre)
Female cub Brezina died and her brother Brezo was left injured and is being treated by staff at the Donana national park in southern Spain.
The third cub, Brisa, has been left with her mother.
The Iberian lynx cubs were born as part of a special breeding programme which had raised hopes of protecting a species threatened with extinction.
Conservation group WWF has warned that the Iberian lynx could become the first big cat since the sabre-toothed tiger to die out - possibly within five years unless swift action is taken.
An environment ministry statement said the injured cub would not be put back in the enclosure while it recovered. The cubs are at the stage of starting to eat solid foods, so it is not essential that it rejoins its mother, Saliega.
Animal experts say fights between sibling cubs are common. In this case the cubs were playing when the two larger ones started getting more aggressive, the ministry said.
The mother realised what was happening and rushed over to separate them, but things happened so quickly, she was too late, the statement added.
It is thought the cub died after being bitten on the neck.
Adults: 75-100cm long, 45-70cm tall, weigh up to 18kg
Live in Spain and Portugal
1960 population - 3,000
2005 population - under 150
Prey on rabbits, small mammals, birds
The ministry, local authorities in Andalusia and the lynx captive breeding programme at the park say the incident is regrettable, but it is a risk when working with wild animals, who have their own rules.
"It is preferable to take this sort of risk than to manipulate the animals," they said.
"Any invasive treatment of the lynx could bring with it serious risks that could threaten the programme and the future reintroduction to nature of any offspring it creates."
Lynx numbers have declined from 100,000 at the beginning of the 20th Century to around just 100-120 in the wild today.
Dam-building, road deaths, hunting and a decline in wild rabbits have led to the cats' downfall.