WASHINGTON (AFP) - An American benefactor has donated US$4.5 million (S$6.2 million)for the giant panda conservation programme at the US National Zoo, where twin cubs were born last month.

David Rubenstein, a co-chief executive of the Carlyle Group asset management firm, pledged to fund the Washington-based programme through 2020.

The zoo is home to female giant panda Mei Xiang, adult male Tian Tian, female two-year-old Bao Bao and an unnamed male cub born on Aug 22. His twin died of pneumonia within a week of birth.

"The National Zoo's panda programme has been a remarkable success - two healthy pandas in just two years - and I am pleased to support it for another five years," Rubenstein said in statement issued by the zoo.

The zoo's panda habitat - its star attraction - is named after the Rubenstein family in recognition of a previous donation to the program made in 2011.

Eleven conservation biologists have also been awarded fellowships funded by Rubenstein to study pandas in the United States and China.

A Twitter account set up in honour of the newborn panda cub reacted gleefully to the news.

"So wait... $4.5m divided by us 4 pandas here... Holy moly!! Am I a millionaire now????? #NeedanAccountant," he tweeted under the handle #houseofcubs.

A member of the zoo-owning Smithsonian Institution's Board of Regents since 2009, Rubenstein has given a total of US$9 million for panda research and another US$2 million in 2013 for Asian elephant research.