Within a decade, three of the four sub-species of the great ape could be wiped out, it says. "Many populations are faced with imminent extinction," said Matthew Woods, of the UN-run Great Apes Survival Project. "It is incredibly serious."
Conservationists have added a new danger to the ever-present threats from hunting, logging and mining: the fallout from elections to be held at the end of this month in the Democratic Republic of Congo (DRC), the vast central African nation which is probably home to more gorillas than any other country.
One sub-species, the eastern lowland, or Grauer's gorilla, lives entirely within its borders. Two others, the mountain gorilla - famous from Dian Fossey's studies and David Attenborough's filmed encounter with them - and the western lowland gorilla, are also found in the DRC.
War has raged within eastern Congo for more than a decade, killing more than four million people in the bloodiest conflict since the First World War. Even now, three years after peace deals were signed, 1,200 people die each day from the continuing violence and war-related diseases. Hundreds of thousands of people have been displaced by the fighting as militia groups rampage through the countryside, raping and pillaging in towns and villages.
One side effect of the conflict has been the devastating impact on the region's gorillas. Refugees unable to grow enough crops to feed themselves have been forced to kill gorillas and other large mammals in order to survive. Conservationists have not only been powerless to protect the animals, with surveys of the remaining gorilla population and other preservation work proving impossible, but several workers have been killed after they were caught up in militia fighting.
The result, in the case of the Grauer's sub-species, is that its numbers are believed to have plummeted by 90 per cent over the past 10 years to just 2,000. Some conservationists believe that the situation is even worse, but violence has prevented them confirming their suspicions.
The most threatened sub-species of all is the Cross River gorilla, which inhabits a tiny forested area of west Africa, but the key to the survival of the rest is thought to be the DRC election, the first in the war-torn country for more than 40 years.
Conservationists believe that only a successful outcome to the election can curb the violence and instability, particularly in the country's eastern districts of Ituri, North Kivu and South Kivu, that have decimated gorilla populations.
"The insecurity threatens the animals and the conservation workers, and it prevents tourism, which is seen by many as the salvation of the apes in this area," said Ian Redmond, chief consultant at the Great Apes Survival Project.
Although there are some fears that an end to the fighting could bring an increase in logging, which would further eat away at the gorillas' natural habitat, the risks of continued anarchy are considered to be greater.
In a region where vast swathes of the population live on less than £1 a day, great apes have proved to be an enormous economic asset.
In Uganda, President Yoweri Museveni has claimed that more than half of the country's foreign exchange earnings are from tourism, in which mountain gorillas are the star attraction. A recent United Nations Environment Programme report on the state of Africa's environment estimated that gorilla tourism brings in roughly $20m (£11m) a year to Uganda and Rwanda, where Western tourists are being lured back with some success after the horrors of the 1994 genocide. There is no immediate prospect, however, of persuading tourists to visit the Democratic Republic of Congo, despite the spectacular scenery of its eastern border country, which is home to mountain and Grauer's gorillas. But Mr Redmond added that the election at least offered some prospect of stability, "and the return to those days of gorilla tourism".
People who had lived through the crisis in DRC remembered what it was like when there were queues of tourists, the conservationist added. "There is a lot of potential... It all depends on political stability. Hopefully there will be enough great apes left."
Species at risk: Only thousands remain in all
Grauer's Gorilla
Also known as eastern lowland gorilla. Forms eastern group with mountain gorilla.
Distribution: Eastern DRC forests. Now inhabits just 13 per cent of its historic range.
How vulnerable: Its habitat is chronically war-torn, and Grauer's gorillas have suffered worst from hunting for "bush meat".
How many left: Estimates vary wildly, from as many as 16,000 to 2,000 or fewer.
Mountain Gorilla
The best-known sub-species, thanks to David Attenborough and the movie Gorillas in the Mist, based on the story of the scientist Dian Fossey.
Distribution: Virunga range of volcanoes on Uganda-Rwanda-DRC border and Bwindi Impenetrable National Park in Uganda.
How vulnerable: Susceptible to a number of threats, from uncontrolled hunting and war to disease, destruction of forest habitat and capture for the illegal pet trade. Considered critically endangered.
How many left: A little over 700.
Western Lowland Gorilla
The most numerous and widespread. All the gorillas in zoos are from this sub-species.
Distribution: Thick rainforests of Gabon and five neighbouring countries. Now inhabits just over half of its former range.
How vulnerable: Suffers from disease and at the hands of poachers. In areas hard hit by the Ebola virus, over 90 per cent have died.
How many left: Estimate of 94,000, though may be higher due to difficulty of surveying habitat.
Cross River Gorilla
The other sub-species in the western group. Differs from western lowland gorilla in skull and tooth dimensions.
Distribution: Eight small and isolated populations, separated by densely settled farmlands, in forested hills on the Nigeria-Cameroon border.
How vulnerable: Rated critically endangered.
How many left: About 200.
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