Liver failure has been blamed for the death of giant panda cub at the National Zoo in Washington DC.
The loss of the six-day-old female bear last month was a blow to wildlife conservation efforts. The odds of the endangered species reproducing in captivity are notoriously slim.
The National Zoo's head veterinarian, Suzan Murray, said at a news conference on Thursday that the cub died from liver necrosis, or death of liver cells.
The problem was probably caused by a lack of oxygen from her underdeveloped lungs, she added.
The cub's birth was a surprise because it had been unclear whether Mei Xiang, aged 14, was still fertile.
Mei Xiang's behaviour has now begun to return to normal, the zoo said.
An estimated 20% of female giant panda cubs born in captivity die within a year, while 26% of males fail to live beyond 12 months.
