Indonesia's air force sent a C-130 plane to transport the 14 apes, each in a metal cage, for the five-hour trip from Bangkok to the Indonesian capital Jakarta.

Most of the orangutans were rescued six years ago on the resort island of Phuket and were sent to an animal sanctuary and breeding centre outside of Bangkok, where two of the animals were born.

Tuenjai Noochdumrong, the director of Thailand's Wildlife Conservation Office, said: "We believe they were smuggled into Thailand and put in private zoos or tourist attractions around Phuket."

Many private zoos in Thailand have animal shows where orangutans perform Thai kick-boxing and other acts.

Thailand is trying to shed its image as a hub for black market wildlife trading and has been cracking down on violators.

Over the past 10 years, Thailand has returned 52 orangutans to Indonesia as part of a programme to fight the illicit wildlife trade and send animals home to their countries of origin, Ms Noochdumrong said.

Indonesia is home to about 90 per cent of the orangutans left in the wild, but half of its rain forest has been cleared in the past 50 years in the rush to supply the world with timber, pulp, paper and more recently, palm oil.

As a result, most of the roughly 60,000 remaining apes live in scattered, degrading forests, putting them in frequent and often deadly conflict with humans.