An endangered female Sumatran tiger died at a zoo in Washington state on Monday after suffering severe injuries during a breeding introduction with a potential mate, zoo officials said.

Kirana, a 6-year-old Sumatran tiger at the Point Defiance Zoo and Aquarium in Tacoma, suffered life-threatening injuries on Friday after being introduced to the zoo’s 2-year-old male Sumatran tiger, Raja, as part of a breeding plan to help save the endangered species, the zoo said.

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"When tigers breed, it’s natural for them to spar with each other and there is typically some level of aggression," said Dr. Karen Goodrowe, the zoo’s general curator. "This level of aggression was far beyond what we would expect with tiger introductions."

Kirana, a 6-year-old female Sumatran tiger at the Point Defiance Zoo and Aquarium in Tacoma, died Monday from injuries she suffered during a breeding introduction with a mate, zoo officials said. (Photo/Katie Cotterill) Point Defiance Zoo & Aquarium.)

The zoo introduced four Sumatran tiger pairs since 2010 and none of those previous pairings resulted in tiger death of serious injury, Goodrowe said.

She called Kirana’s death "heartbreaking," saying that staff had approached the pairing of Kirana and Raja "slowly and carefully" over many months.

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The two tigers had been kept physically separated by a mesh door while still being able to see and smell each other to develop familiarity, the zoo said. Once both tigers showed signs they were comfortable with each other, keepers removed the mesh door and allowed the pair to meet.

After witnessing Kirana in distress, the zoo said that keepers quickly separated the two tigers and addressed her injuries.

Despite Kirana’s health appearing to improve on Sunday, the endangered tiger died the following day, the zoo’s head veterinarian Dr. Karen Wolf said. A necropsy confirmed Kirana suffered substantial trauma from injuries and a bacterial infection.

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"The loss of Kirana is a tragedy for our zoo family, our community, and our world," said Point Defiance Zoo Director Alan Varsik. "With just a few Sumatran tigers left on this earth, we need to do everything we possibly can to help them survive."

There are an estimated 400 Sumatran tigers left in the wild on the Indonesian island of Sumatra, according to the zoo, with only 77 of the endangered animals residing in North American zoos.

In addition to Raja, there are three other Sumatran tigers living in the Point Defiance Zoo and Aquarium’s Asian Forest Sanctuary: Bandar, 8, Kali, 8, and Indah, 6.