The shooting of a gorilla at a zoo in Cincinnati after a boy fell into the enclosure has sparked a backlash.
A special response team at Cincinnati Zoo shot and killed a male gorilla called Harambe who grabbed the four-year-old after he fell 12ft into the exhibit moat.
Authorities said the youngster is expected to recover after being picked up out of the moat and dragged by the gorilla for about 10 minutes.
Using the hashtag #JusticeForHarambe, many are saying the gorilla should not have been killed as he did not intend to hurt the boy, while others are blaming the parents, saying they should be held responsible for not looking after their child.
The boy was taken to Cincinnati Children's Hospital Medical Centre after the incident.
Director Thane Maynard said the zoo's dangerous animal response team decided the boy was in "a life-threatening situation" and they needed to put down the 17-year-old 400 pound-plus (180kg) gorilla.
"They made a tough choice and they made the right choice because they saved that little boy's life," he said. "It could have been very bad."
Maynard added: "The zoo family is going through a painful time, and we appreciate your understanding and know that you care about our animals and the people who care for them."
Investigations are ongoing, but zoo officials believe the boy crawled through a railing barrier, then fell into the moat.
Maynard said the gorilla did not appear to be attacking the child but that it was "an extremely strong" animal in an agitated situation.
He said tranquillising the gorilla would not have knocked it out immediately, leaving the boy in danger.
Maynard said it was the first time the team had killed a zoo animal in such an emergency situation, and he called it "a very sad day" at the zoo. The lowland gorilla is an endangered species.
Harambe came to Cincinnati last year from the Gladys Porter Zoo in Brownsville, Texas.
The zoo said its Gorilla World area would remain closed until further notice.
The zoo prides itself on its work in protecting endangered species, and has been part of successful captive breeding efforts in recent years in the effort to save the endangered Sumatran rhino. It is home to nine western lowland gorillas.