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Three tiny polar bear cubs are being left to starve to death after a zoo decided not to rear them by hand if their mother continues to neglect them.
Mother bears Vera and Wilma gave birth three weeks and five weeks ago at Nuremberg Zoo in southern Germany.
It is thought they have six cubs between them.
Wilma is displaying the signs of being a good mother, but Vera shows no interest in her young.
She frequently strolls out of her cave, where the hungry cries of her babies can be heard from within, and she lazes for hours outside her lair.
It was such neglect from his mother that propelled a cub called Knut to international fame at another German zoo last year.
He was abandoned by his mother at birth, and animal rights activists said he should die rather than be raised by humans.
But Berlin Zoo officials disagreed and Knut became a sensation. He has been on the cover of Vanity Fair magazine and a Hollywood film company is negotiating the rights to his story.
Nuremberg, however, is taking a hard line on Vera's cubs. As people bombard the zoo with demands that keepers intervene unless Vera's mothering skills pick up, deputy director Helmut Maegdefrau says he wants "no Knutmania" at the zoo.
"We expect to be branded as being cruel to animals. The fact is, in nature, if something goes wrong, it goes wrong," he said.
"If you don't let the mothers practise, they'll never learn how to bring up their cubs. We're cautiously optimistic. Vera does come out of her cave occasionally but the cubs are crying loudly, and she walks back in when they do. If we were to keep checking, we would disturb them and make it more likely that something goes wrong."
He said he wasn't opposed to hand-rearing in principle but that it had to be decided case by case.
"Berlin Zoo did a terrific job hand-rearing Knut from day one. But we want to avoid Knutmania at all costs. If people spend hours queuing up to see a polar bear cub, there's something wrong. We've got a baby giraffe, too, that's just as cute."
Berlin Zoo director Bernhard Blaskiewitz said he disagreed with the stance taken in Nuremberg.
"This is not some new fad," he said. "We hand-reared a bear in 1986 that now lives in Serbia. That is responsible breeding and care. We have no concerns for the welfare of Knut."
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