WASHINGTON - A giant panda cub born last weekend at the National Zoo in Washington has died.

Zoo officials said the cub was found dead Sunday morning after panda keepers heard sounds of distress from its mother, Mei Xiang.

   Staffers were able to retrieve the cub about an hour later. The cause of death is unknown. The cub appeared to be in good condition, and there were no outward signs of trauma or infection.

   Zoo director Dennis Kelly calls the cub's death "devastating" for the entire staff.

"It's hard to describe how much passion and energy and care has gone into this," he said.

   The cub had been a surprise at the zoo. Fourteen-year-old Mei Xiang had five failed pregnancies before giving birth.

   Panda cubs are born about the size of a stick of butter and are delicate infants. They're at risk for infections and so small that it's not unheard of for panda moms to accidentally crush their young.