Mei Xiang, the female giant panda at the National Zoo in Washington, is pregnant and could give birth in the next few days, the zoo announced on Monday.

"Keep your paws crossed!" the U.S. capital's zoo said on its Twitter feed.

It said that veterinarians had detected a fetus during an ultrasound of the 22-year-old giant panda.

"Her fetus was kicking + swimming in the amniotic fluid, and its spine + blood flow were visible," the zoo said. "We hope to have a healthy cub in the coming days!"

"In the middle of a pandemic, this is a joyful moment we can all get excited about," Don Neiffer, the zoo's chief veterinarian, said in a statement.

Mei was artificially inseminated on March 22 with frozen semen from the zoo's male panda, Tian Tian. She has given birth to three surviving cubs, all of which were sent to China under a cooperative breeding agreement with Beijing.

China lends pandas to zoos around the world – a program dubbed "panda diplomacy." Once young pandas reach the age of four, they are repatriated to breed with other pandas at sanctuaries in China.

The animals are considered "vulnerable" to extinction by the International Union for Conservation of Nature.

The National Zoo's panda enclosure is currently closed to visitors, but 24-hour "panda cams" are in use to observe their behavior.