A giant panda born in the United States has given birth to twin cubs in Chengdu, capital of southwest China's Sichuan Province.

Su Lin gave birth to the twins at 4:30 p.m. and 8:45 p.m. on Sunday at the Giant Panda Protection and Research Center of China, researchers with the center said on Monday.

One cub, weighing 173.8 grams, is male but researchers have not been able to tell the gender of the other as Su Lin has been holding it since it was born.

Su Lin was born in August 2005 at San Diego Zoo in the United States and returned to China in 2010. Her parents were sent to the United States for panda breeding research programs. Under the program agreement, all pandas born overseas belong to China.

Su Lin was fertilized by male panda Yuan Yuan through natural mating on March 20 before artificial insemination with the sperm of another male, Lu Lu.

The cubs will receive paternity tests in one or two years to find out whether Yuan Yuan or Lu Lu is the real father.X Forty-nine cubs were born last year in China, with 42 surviving, a record for giant panda breeding in the country.

Thanks to the development of breeding technology, the number of captive-bred giant pandas around the world had hit 376 by the end of 2013. It is estimated that about 1,600 pandas live in the wild.