OSLO - Twenty-five species of humans' closest living relatives - apes, monkeys and lemurs - need urgent protection from extinction, a report by international conservation groups said on Monday.

Many of the primates, from the Ecuadorean brown-headed spider monkey to the eastern black-crested gibbon in China and Vietnam, are under threat from human destruction of forests, from hunting and from illegal wildlife trade.

The study said five of the 25 most endangered primates were from Africa, six from the Indian Ocean island of Madagascar, nine from Asia, and five from South America, including the Ka'apor capuchin monkey in Brazil.

"Mankind's closest living relatives...are on the brink of extinction and in need of urgent conservation measures," said the report by groups including the International Union for Conservation of Nature (IUCN).

Lemurs in Madagascar were among the most threatened after years of political unrest on the island, said Christoph Schwitzer, head of research at the Bristol Conservation and Science Foundation, one of the authors.

"The rarest lemur, the northern sportive lemur, is now down to 19 known individuals in the wild," said the report, presented to coincide with a meeting of the UN Convention on Biological Diversity in Hyderabad, India.

The scientists said that conserving primates, of which there are 633 known species, was important for the wider fabric of nature.

Primates "often serve as seed dispersers and help to maintain forest diversity", said Russell Mittermeier, a chair of the primate specialist group at the IUCN and president of Conservation International.

"It is increasingly being recognized that forests make a major contribution in terms of ecosystem services for people, providing drinking water, food and medicines," he wrote.

The experts said there was some good news: no primate species has been lost to extinction in the 20th or 21st centuries. And numbers were rising for some, such as India's lion-tailed macaque and Madagascar's greater bamboo lemur.

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