A giant panda at the Atlanta zoo has given birth to twin cubs. This has surprised officials because they had been expecting the birth of a single cub.

Zoo officials say twin cubs have never been born at Zoo Atlanta, and the two cubs are the first to be born in the United States in 2013. They haven't confirmed the gender of the cubs.

The zoo will work with experts in China to decide on how to name the twins after 100 days.

The cubs are the fourth and fifth to be born to mother Lun Lun and father Yang Yang, both 15 years old.

The couple were sent to Zoo Atlanta in 1999. Their first born is at China's Chengdu Research Base of Giant Panda Breeding, and the other two cubs are on site at the zoo, but they are being prepared to move to China later in the year.