The only animal to have escaped is a "harmless" grey wolf that fled about a month ago and has still been not found, said Supoj Methapiwat, director of the zoo's animal management division.

Nikom Putta, a coordinator of the Northern Wildlife Protection Foundation, said earlier yesterday the zoo had said it would give a Bt20,000 reward to anyone who could bring the hyenas back.

Nikorn claimed one hyena was found in a garbage pit by villagers on Wednesday and was returned to the zoo. The other was still at large, he said.

"This is not the first time flesh-eating animals have broken loose from the zoo. Previously a tiger escaped. They are very dangerous to us," he said.

Nikom said the incidents showed the animals' cages were not suitable to prevent them getting free. The animals could spread diseases to people, he warned.

But Supoj said no hyenas or dangerous animals had ever broken out of the zoo.

He admitted that a grey wolf had escaped a month ago when it became alarmed while on show. He had informed nearby villagers that the wolf was not dangerous and the zoo provided tools to try to recapture it.

Supoj said the animal captured by villagers on Wednesday was not a hyena but a wild fox, which had not escaped from the zoo. He denied ever offering a Bt20,000 reward.