A female Malayan tiger at the San Diego Zoo has been fatally mauled by her intended mate during an attempt to breed.
The female tiger, named Tiga Tahun, died of neck injuries and breathing difficulties, the zoo said.
The encounter "began with positive interaction between the two big cats", the zoo said in a statement.
"Unfortunately this changed quickly and zoo-keepers were unable to separate the two animals."
Saturday's attempt was the first breeding encounter for either animal, the only Malayan tigers at the facility.
No visitors saw the attack.
The tigers had rotated between being on exhibit and in their bedrooms, making them familiar with the other's scent, a zoo spokeswoman said.
They had seen each other often and even touched noses, separated by a barrier - leading zoo-keepers to believe the timing was right.
Tiga Tahun was born in 2009 at the Bronx Zoo, while her intended mate, Connor, was born at the San Diego Zoo in 2011.
Fewer than 500 Malayan tigers are believed to be living in the wild worldwide, and another 60 live in captivity in North American zoos.
Fatal attacks are rare, but behaviour can be unpredictable during breeding, experts say.
