The new bears arrived 11 months after the zoo in Washington sent its three highly popular pandas — 25-year-old Mei Xiang, 26-year-old Tian Tian and their cub Xiao Qi Ji — home to China.

Pairs of breeding pandas at zoos in Memphis, Tennessee, and San Diego, California, already have returned to China, and the four pandas at the zoo in Atlanta, Georgia, left for China last week.

President Xi Jinping expressed support for continuing the giant panda conservation programs during a visit in November last year to San Francisco for a China-US summit and the 30th Asia-Pacific Economic Cooperation Economic Leaders' Meeting.

Two pandas — Yun Chuan, a 5-year-old male, and Xin Bao, a 4-year-old female — arrived at the San Diego Zoo in August. They were the first pandas sent to the US in more than two decades. Two other pandas have been promised to San Francisco.

Liu Pengyu, a spokesman for the Chinese embassy in Washington, said the US was among the first countries to work with China on panda conservation.

"Since we started the cooperation program with the National Zoo in 2000, positive outcomes have been achieved in panda conservation and breeding, disease prevention and treatment, and public awareness," Liu told China Daily on Monday.

Together, the researchers have successfully bred 17 panda cubs and solved a number of technical challenges, he added.

"The current round of cooperation will focus on prevention and treatment of major diseases, and protection of habitats and wild giant panda populations," he said. "We hope the arrival of the pandas will inject fresh impetus into exchanges between China and the US, and help to stabilize the broader bilateral relationship as well."

Elliott L. Ferguson II, president and CEO of Destination, DC, said: "The giant pandas are an iconic part of the Washington, DC, story, both for locals and incoming travelers alike. The interest and excitement associated with their return directly benefits the entire city, bringing further interest and visitors to our hotels, restaurants and other attractions."

Agencies contributed to this story.