Dozens of the animals died after they were treated with anti-parasitic medicine

A Japanese zoo has launched an investigation after apparently killing 31 of its 40 squirrels by mistake with treatments meant to kill parasites, officials said.

Keepers at the Inokashira Park Zoo in Tokyo treated the animals with anti-parasitic medicine on 4 December as part of a sanitary precaution, while also spraying insecticide over their nest boxes.