One of the last northern white rhinos on the planet has died in a reserve in Kenya, highlighting the species' risk of extinction.

The male rhino, named Suni, "was probably the last male capable of breeding," according to Dvur Kralove zoo in the Czech Republic, via the Agence France-Presse (AFP).

Over a million years ago, the northern white rhino roamed across Chad, Uganda, the Democratic Republic of Congo and South Sudan. In 1960, they numbered at about 2,000, until poachers in the 1970s and '80s hunted them down to a mere 15. Their horns were highly prized for traditional Chinese medicine. Now, there are only six members of the species left, all of them in captivity.

The number had been seven until Friday, when 34-year-old Suni was found dead by rangers at the Ol Pejeta Conservancy in Kenya. The cause of death is still unknown, but he is not believed to be a victim of poaching. And to make matters worse, he was only one of two breeding males left in the world.

"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.

Suni was brought to the conservancy in 2009 with four other northern white rhinos for a breeding program, an operation dubbed "the last chance of survival," according to the AFP. Attempts have been made to artificially inseminate these animals, but none have been successful.

And so, with Suni gone, the fate of this rare species now lies in the hands of the three rhinos left at Ol Pejeta Conservancy - one male and two females.

"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 said in the statement.

Lucky for the southern white rhinoceros, they are faring much better, with an estimated 17,000 wild-living animals.