Many of man's closest living relatives - apes, monkeys, lemurs and other primates - are on the brink of extinction, according to a new report released at the UN's Convention on Biological Diversity meeting this week in the Indian city of Hyderabad.

"Whilst we haven't lost any primate species yet during this century, some of them are in very dire straits," said Dr. Christoph Schwitzer, of the Bristol Conservation and Science Foundation (BCSF), which generated the report with three other conservation groups.

Among the 25 most endangered primates, six are from Madagascar, five from Vietnam, three from Indonesia and two from Brazil.

Lemurs are particularly at risk: 91% of the 103 species and subspecies are threatened with extinction, "one of the highest levels of threat ever recorded for a group of vertebrates," the report said.

Madagascar's rarest lemur, the northern sportive lemur (Lepilemur septentrionalis), is now down to a population of just 19 animals in the wild.

Aside from being a big draw for ecotourists (and thereby generating revenue for some nearby communities), primates also play an important part in maintaining the world's tropical forests, where they disperse tree and plant seeds through their activity.

But human activity is putting them in peril: habitat destruction, illegal wildlife trade and bush meat hunting.

The report calls for urgent conservation measures, which have been shown to succeed in the past.

Several species, such as India's lion-tailed macaque (Macaca silenus) and Madagascar's greater bamboo lemur (Prolemur simus), have been removed from the biennial list since its inception in 2006 because their statuses have improved due, at least in part, to the increased attention this list brings.