National Zoo officials say the 6-day-old panda cub that died had abnormalities on its liver and fluid in its abdomen, but they don't yet know the cause of death.

Smithsonian National Zoological Park Chief Veterinarian Dr. Suzan Murray (R) and zoo Director Dennis Kelly. (Chip Somodevilla/Getty Images)

Officials say they believe the cub was female, although they're not completely sure.

PREVIOUS: Newborn Panda Dies At National Zoo

They expect to know more once a necropsy is completed within two weeks.

Zoo officials said the 4-ounce cub showed no obvious signs of distress before making its final recorded noise Sunday morning. The cub's mother, Mei Xiang (may shahng), made an unusual honking sound that her keepers interpreted as a distress call.

Zoo officials say Mei Xiang has begun to eat again and has come out of her den. They say she's cradling a plastic toy at night in what may be a display of maternal instinct.

(Copyright 2012 by The Associated Press.  All Rights Reserved.)