Six Sumatran orang-utans that were smuggled into Malaysia and displayed at a theme park for almost four years have been flown home.

The primates were flown to Jakarta on Saturday aboard a Malaysia Airlines flight dubbed the "Orang-utan special", and transferred to a Garuda flight for their final destination in a Medan wildlife sanctuary, the New Straits Times said.

The decision to return the orang-utans, aged between three and four years old, was made after the wildlife department conducted a DNA finger-printing exercise following a tip-off.

Theme park

Malaysiakini has in May published a series of reports on suspected smuggled orang utans held in Malacca's theme park A'Famosa Resort.

Some of the orang utans had for some years been featured in shows at the Kuala Lumpur Bird Park, which was later cancelled .

The Sumatran orang-utan is listed on Appendix 1 of the Convention on International Trade in Endangered Species (Cites) which means they are critically endangered status and cannot be traded.

An estimated 7,500 Sumatran orang-utans remain in the wild.