Panda cub
The smaller panda cub has died after being rejected for feeding by its mother Mei Xiang Twitter

Washington's National Zoo has reported that one of its two newborn panda cubs has died. Giant panda Mei Xiang gave birth to the two cubs on Saturday August 22.

The twins were born four hours apart. The small cub weighed 86 grams when it was born, while the larger cub weighed 138 grams. Experts expressed their concerns for the smaller cub, after the mother appeared to give preference to the stronger cub.

The weaker cub was kept in an incubator while the other was kept with the mother. It was decided the twins would be rotated so she could nurse and bond with each of them in turn. However, it was found that Mei Xiang had rejected attempts by keepers to swap the cubs.

Posting the sad news on Twitter, The National Zoo said: "We are sad to report that the smaller of the two panda cubs has died. We will continue to provide updates on social media w/ #Pandastory." The surviving cub appears to be strong and behaving normally, said the zoo.

The 17-year-old female giant panda was artificially inseminated from two potential fathers - Hui Hui, a panda in China, and the National Zoo's Tian Tian. She gave birth to two other cubs in 2005 and 2013 and both survived. Mei Xiang's first cub, Tai Shan, returned to China in 2010. Her second cub, Bao Bao, just celebrated her second birthday.

Giant pandas are one of the most endangered species in the world and are notoriously hard to breed in captivity.

The National Zoo is one of only four zoos in the US to have pandas, which are on loan from China.