Image caption Mei Xiang had five failed pregnancies before giving birth to the cub

A week-old giant panda cub has died at Washington DC's National Zoo, with the cause of its death not immediately apparent.

Zoo staff were alerted to the cub's plight after its mother, Mei Xiang, was heard making sounds of distress.

The tiny cub was removed from the panda enclosure but attempts to revive it proved unsuccessful.

The zoo said the cub weighed just under 100g (3.5oz), and that there were no obvious signs of injury or infection.

In a statement, the zoo said: "We are broken-hearted to share that we have lost our little giant panda cub.

"Panda keepers and volunteers heard Mei Xiang make a distress vocalisation at 09:17 (13:17 GMT) and let the veterinarian staff know immediately.

"They... were able to safely retrieve the cub for an evaluation at 10:22, which we only do in situations of gravest concern.

"The veterinarians immediately performed CPR and other life-saving measures, but sadly the cub was unresponsive."

Fourteen-year-old Mei Xiang had five failed pregnancies before giving birth to the cub, which was conceived by artificial insemination after she and the zoo's male, Tian Tian, failed to mate.

Only one panda cub has survived at the zoo in the past.