A male polar killed a female polar bear while attempting to mate at the Detroit Zoo in the US state of Michigan, staff said Tuesday.

Scott Carter, the chief life sciences officer of the zoo, told WDIV-TV, a local news channel, that an aggressive encounter while mating led to the death of 20-year-old Anana by the male polar bear Nuka.

"When bears and other large carnivores breed it is sometimes described in nature as an aggressive encounter. It usually involves physical control of the female by the male, which usually includes him holding her by the back of the neck," he said.

A sudden and 'tragic event'

Staff at the zoo said that they were devastated by the tragic event. Nuka and Anana had previously lived together in 2020 without any incident. They were apart for a few months and re-introduced to each other last week as part of a conservation program for captive animal populations.

Carter said that Nuka, who has been in the zoo since 2011, had previously bred with other bears without showcasing harmful behavior. Nuka had fathered twin cubs recently with another polar bear, Suka.

The Detroit zoo last witnessed the killing of one animal by another back in 1988 - that incident also occurred with polar bears.

The Associated Press contributed to this report