There are only six northern white rhinos left in the world, conservationists have warned.
The news came as a white rhino died at the Ol Pejeta Conservancy near Nairobi, Kenya.
The 34-year-old animal, called Suni, was one of just two breeding male rhinos left.
He was taken to Africa from a zoo in Czech Republic, where he was born in 1980, to be a part of a breeding program.
The cause of his death is still unknown. Suni's father, also 34, died of natural causes in 2006.
"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.
"We will continue to do what we can to work with the remaining three animals in Ol Pejeta in the hope that our efforts will one day result in the successful birth of a northern white rhino calf."
According to WWF, there are only four northern white rhinos left in the world. Unconfirmed reports state there are also some in Sudan.
Rhinos and Poaching
The main cause of the white rhino population decline is poaching, animal rights activists said.
As late as 1960, there were more than 2,000 animals remaining. By 1984, only about 15 individuals had survived.
Rhinos are killed for their horn, widely used in Vietnam and China in traditional medicine.
Namibia, home to the largest concentration (1,750 out of nearly 5,000) of the black rhino subspecies, now allows dehorning as a practice to halt poaching and prevent the animals from being killed.
In neighbouring South Africa, one of the countries worst affected by rhino poaching, at least 558 rhinos have been killed since the beginning of 2014. Last year, the number of rhinos killed was 1,004.
According to campaigners, 1,000 rhinos are killed each year by poaching, and the animals could be extinct in 20 years.