WASHINGTON – The 6-day-old giant panda cub that died at the National Zoo had liver abnormalities and fluid in its abdomen, but zoo officials said Monday that they don't yet know the cause of death.

The cub, believed to be female, died Sunday morning, less than a week after its birth surprised and delighted zoo officials and visitors. The zoo had all but given up on the panda mother's chances of conceiving.

A necropsy on the cub will be completed within two weeks, and officials expect to have a definitive answer on the cause of death. Panda cubs are about the size of a stick of butter at birth and are susceptible to infections and fatal injuries.