The killing of a gorilla at a zoo in the US city of Cincinnati after a four-year-old boy fell into its enclosure has triggered outrage on social media.
Many said male gorilla Harambe should not have been shot dead as he did not intend to hurt the boy, some using the hashtag #JusticeForHarambe.
Others said the parents should be held responsible for not looking after their child during Saturday's incident.
Zoo officials shot dead the gorilla after he grabbed and dragged the boy.
The zoo said it had taken this action against the 400lb (180kg) gorilla as the situation was "life-threatening".
Twitter user StrayanRepublic, wrote: "#HARAMBE wasn't dragging him to kill him... he was protecting the child from the threat of screaming tourists. @Xoxjlove @CincinnatiZoo."
Kenz, another user, posted this message: "#JusticeForHarambe its so sad that an endangered animal had to be put down because of careless parenting."
Meanwhile, Andrue wrote: "Why don't zoos have instant acting tranquilizer? First those 2 lions now Harambe #JusticeForHarambe."
He was referring to last week's incident when two lions were shot dead in a zoo in Chile after a man entered their pen in an apparent suicide attempt.
More than 60,000 people have also signed a special petition, calling for the boy's parents to "be held accountable for the lack of supervision and negligence that caused Harambe to lose his life".
Cincinnati zoo has temporarily shut its gorilla exhibit following the incident.
The boy had climbed through a barrier and fallen about 3m (10ft) into the moat. Video shows the boy being dragged through the shallow moat. The gorilla then stops, with the child below him and looking up at him.
But reports say this was only a partial picture, and the boy was dragged by the 17-year-old male western lowland gorilla for about 10 minutes.
He was taken to a local hospital and although no information about his condition has been released, it is believed he will fully recover.
Zoo director Thane Maynard said: "[The officials] made a tough choice and they made the right choice because they saved that little boy's life. It could have been very bad."
He said a tranquilliser would not have had a quick enough effect.
Mr Maynard said that although the boy was not under attack, he "certainly was at risk".
He added: "We are all devastated that this tragic accident resulted in the death of a critically endangered gorilla. This is a huge loss for the zoo family and the gorilla population worldwide."
Harambe was born in captivity in Texas and moved to Cincinnati zoo in 2014, where it was hoped he could be part of a breeding programme. Cincinnati zoo has had the largest number of western lowland gorilla births in the US.
In a similar incident in 1986 on the island of Jersey, a Crown dependency of the UK, a five-year-old boy fell into a gorilla enclosure.
He lost consciousness and a silverback gorilla called Jambo famously stood guard over him, protecting him from other gorillas and stroking his back. When the boy came round he started to cry and the gorillas retreated, allowing keepers and an ambulanceman to rescue the child.
A life-sized statue of Jambo fetched £18,000 ($26,000) at auction and he even appeared on Jersey stamps.
The western lowland subspecies inhabits west African rainforests and is the most numerous, although exact figures are not known. There are more than 500 in zoos worldwide.
The shooting of the lions last week in Santiago, Chile, brought criticism from activists. Zoo officials said no fast-activating tranquillisers were available.
The man had jumped into the enclosure and stripped naked.