Zoo officials on May 29 shot dead a gorilla after a four-year-old boy fell into its enclosure in the US city of Cincinnati.

The killing of a gorilla at the Cincinnati Zoo after a 4-year-old boy tumbled into the ape's enclosure triggers outrage and questions about safety, but zoo officials say the decision to use lethal force was a tough but necessary choice.

Zoo officials shoot dead a gorilla after it grabbed a four-year-old boy who fell into its enclosure in the US city of Cincinnati.