Two Rare Sumatran Tiger Cubs Born at National Zoo in Washington D.C. [LIVE STREAM]

Two rare Sumatran tiger cubs were born Monday at the Smithsonian National Zoo in Washington D.C., providing a welcome addition to a critically endangered species whose numbers in the wild are only about 500 worldwide.

The mother tiger, known as Damai, is reportedly being a "great mom" and nursing the cubs, both of which appear to be healthy. There are fewer than 70 Sumatran tigers in captivity in North American zoos.

Damai gave birth to the cubs on Monday, Aug. 5, the first being born at 6:15 p.m. the second followed two hours and fifteen minutes later, the National Zoo announced Thursday.

"We are giving Damai time to bond with and care for her cubs," National Zoo said in a statement on its website. "They most likely will not be on exhibit until late fall."

Sumatran tigers have a short gestation period of about 100 days. Cubs are born blind and weigh between two and four pounds, according to the conservation group Sumatran Tiger Trust.

Zookeepers begin to closely monitor Damai in June after she began gaining weight and exhibiting behaviors consistent with pregnancy. Zoo staff were able to train the tiger to participate in an ultrasound, which they used to confirm her pregnancy on June 21.

The cubs are Damai's first litter, sired by by the Zoo's 12-year-old male Sumatran tiger Kavi. The two endangered cats mated several time between December 2012 and April of this year.

"It's taken more than two years of perseverance getting to know Damai and Kavi and letting them get to know each other so that we could reach this celebratory moment," said Zoo biologist and great cats curator Craig Saffoe. "All I can do is smile because the team has realized our goal of producing critically endangered tiger cubs. Damai came to us as a young tiger herself, so it's really special to see her become a great mom."

Speaking with NBC's TODAY, Saffoe said Zoo team members were worried when the two grown tigers were introduced to breed. If they didn't take a liking to one another, one or both of them could have been injured, or worse, he said.

"Our little female has a little bit of spice to her, and she slapped around our boy quite a bit, but he turned out to be the coolest cat."

Two webcams are set up for people to peek in on the new tiger cubs and their mom.