The Swiss-based International Union for Conservation of Nature (IUCN) said there were just 30 of them left in April 2003, and only four confirmed animals as of August 2006.

"Worryingly, recent fieldwork has so far failed to find any presence of these four remaining rhinos," Martin Brooks, head of its African Rhino Specialist Group, said in a report.

"Unless animals are found during the intensive surveys that are planned under the direction of the African Parks Foundation, the sub-species may be doomed to extinction."

White rhinos are targeted by poachers for their horns, which fetch high prices in Yemen, where they are made into dagger handles, and in the Far East, where they are coveted for their supposed medicinal qualities.

But wildlife protection is almost impossible in the eastern DRC due to militia violence that still haunts the region five years after a war that killed some 4 million people, mostly from hunger and disease.

Authorities there arrested a senior game ranger in March suspected in the slaughter last year of several rare mountain gorillas in Congo's oldest national park, Virunga.

And last month, a conservation group said soldiers, rebels and local villagers in Virunga had recently killed 14 elephants in as many days to meet surging Chinese demand for ivory.

In the thick forests of Garamba, further north, the shadowy bands of hunters include heavily-armed guerrillas from northern Uganda's Lord's Resistance Army.

Elsewhere on the world's poorest continent, the news for rhinos was much better, said the IUCN, which produces estimates of wild animal populations that are considered highly authoritative.

Conservation efforts including translocation and the stemming of poaching had boosted overall numbers of white rhinos to 17,480 last year from 14,540 in 2005, it said.

Numbers of the smaller, more aggressive African black rhino rose to 4,180 from 3,730, although it is still listed as critically endangered by the IUCN. (Editing by Caroline Drees) (For Reuters latest environment blogs click on: http://blogs.reuters.com/environment/)