Thousands of great apes are killed or trafficked into "slavery" each year in a multi-million dollar illegal trade that is driving some of man's closest relatives towards extinction, conservationists said Tuesday.

"Organised criminal networks, involving corrupt government officials, threaten great apes with extinction by trafficking them to be used as performers or pets," said Daniel Stiles, from the Project to End Great Ape Slavery (PEGAS), a campaign group launched Tuesday to raise awareness of their plight.

"To capture one infant ape, as many as 10 apes are ruthlessly killed... The orphans are sold into what can only be called slavery, as great apes are the closest species to humans," he added.

Hundreds of great apes -- including chimpanzees, gorillas and orangutans -- have been "brutally captured" and sold to countries including Armenia, China, Egypt, Russia, Thailand and the United Arab Emirates in an "insidious trade", the group said.

"The toll on wild ape populations over the past ten years numbers in the thousands, threatening some species with extinction if current trends are allowed to continue," Stiles said at the only chimpanzee sanctuary in east Africa, some 230 kilometres (140 miles) north of the Kenyan capital Nairobi.

"It must stop for conservation and moral reasons," he added.

Karl Ammann, a wildlife trade investigator, said some governments were ignoring the crime.

"If there's illegal trafficking of wildlife, you expect authorities to arrest all those involved... but it is not happening," he told reporters, noting that in China 84 illegal chimpanzees had been found in zoos, but that nothing had been done.

The campaigners alleged that some African nations sold fraudulent export permits to allow protected animals to be trafficked commercially, "to be trained as amusement park performers, or used to attract customers to for-profit zoos, or to become pets of the rich and powerful."

A joint UN and Interpol report released last month warned that while the greatest threat to apes is habitat loss, the illegal trade in the animals is "widespread", with over 22,000 great apes estimated to have been taken between 2005 and 2011.