While there are thousands of southern white rhinos still roaming the plains of sub-Saharan Africa, decades of rampant poaching have drastically cut northern white rhino numbers.
Suni, a 34-year-old who was the first northern white rhino to be born in captivity, was found dead on Friday by rangers at the Ol Pejeta Conservancy, about 250 km north of Nairobi.
The conservancy said Suni was not poached, but the cause of his death was unclear. It added that he was one of the last two breeding males in the world as no northern white rhinos are believed to have survived in the wild.
"Consequently the species now stands at the brink of complete extinction, a sorry testament to the greed of the human race," the conservancy said in a statement.
Breeding program tries to prevent extinction
The Kenya Wildlife Service vets will conduct a post mortem in the coming days, the conservancy added. Suni's father, Suit, died in 2006 of natural causes, also aged 34.
Born in the Dvur Kralove Zoo in Czech Republic, Suni was in 2009 one of the four northern white rhinos brought from that zoo to the Ol Pejeta Conservancy to take part in a breeding program to try to prevent the extinction of the species.
Wildlife experts had hoped the 90,000-acre private wildlife conservancy, framed on the equator and nestled between the snow capped Mount Kenya and the Aberdare mountain range, would offer a more favourable climate for breeding.
"We will continue to do what we can to work with the remaining three animals on Ol Pejeta in the hope that our efforts will one day result in the successful birth of a northern white rhino calf," the conservancy added.
Wildlife conservationists have struggled to reverse a decline in numbers of several African species, undermined by ferocious poaching by gangs which mostly ship the ivory to Asia.
Last year, 59 rhinos were poached in Kenya, a country famous for its sprawling Maasai Mara game park and abundant wildlife.
Rhino horn sold on the streets of major Asian cities was last year more valuable than gold or platinum, with traders asking for about $65,000 per kg of rhino horn.