(REUTERS) - A newborn gorilla at the North Carolina Zoo was found dead in its cage early on Wednesday, still wrapped in the arms of his mother, who may have accidentally rolled over on the infant during the night, officials said.

Calling it "one of the saddest events in the history of the North Carolina Zoo", officials said they may never know the official cause of death for the unnamed western lowland gorilla. Zoo staff believes that the first-time mother, Acacia, may have rolled over the male newborn while she was sleeping.

Zoo workers made the discovery during an early morning check of the pair, who were under 24-hour care after the Sunday birth.

The newborn's arrival marked the third gorilla in the past year born at the zoo.

The father of all three, 21-year-old Nkosi, arrived at the zoo in 2008 as part of the Gorilla Species Survival Plan of the Association of Zoos & Aquariums.

The high birth rate was celebrated as a rarity, both for the zoo and for the United States (US), as only an average of five gorillas are born in US zoos annually, zoo officials said.

The other two gorillas born in August 2012 are healthy and on display at the zoo.

Primates often lose their firstborn due to inexperience or accidents, but successfully raise more offspring later, said Mr Adrian Fowler, the zoo's Curator of Mammals.

"Gorillas face exactly the same risks during the early neonatal period as humans and, even in that field, the causes of early infant death often remain unknown," Mr Fowler said.

The gorilla was born by Caesarean section after Acacia struggled through 24 hours of labor, and the two were bonding well, zoo officials said.

The infant was healthy and the mother had recovered from the surgery well enough to take care of him, said Mr Mike Loomis, the zoo's chief veterinarian.

"It's really unfortunate," Mr Loomis said. "But those are the chances you have to take in these kind of situations. We have to give the mother every opportunity to care for the baby on her own."