(CNN) Malaysia's last male Sumatran rhino has died, leaving behind just one female of the same rare species in captivity in the country.
The Borneo Rhino Alliance (BORA) confirmed the animal's death in a statement on Facebook on Monday, saying: "It is with heavy hearts that we share the tragic news that Tam, Malaysia's last male Sumatran rhino, has passed away."
Tam had been suffering from organ failure before his death, BORA said.
Sumatran rhinos are the world's smallest rhinoceros species, standing at around 4 feet 3 inches high, when fully grown. They are the only Asian rhinos with two horns, and are covered in hair.
The animals are found in Indonesia, Malaysia's Sabah state (part of the island of Borneo) and peninsular Malaysia; some are also thought to live in southern Thailand, according to the World Wildlife Foundation (WWF).
It is unclear precisely how many Sumatran rhinos remain, but experts at the International Rhino Foundation believe there are fewer than 80 still in the wild.
BORA describes the rhinos as "functionally extinct," meaning that the few animals remaining are insufficient to save the species from dying out.
Tam's death means there is only one Sumatran rhino, a female called Iman, left in Malaysia.
The World Wildlife Foundation (WWF) considers the creatures to be critically endangered as a result of poaching and habitat fragmentation.
Tam was captured and brought to live in Sabah's Tabin Wildlife Reserve. It was hoped he would breed with captive female rhinos, but these hopes were dashed when it was discovered that the two female rhinos at the reserve were infertile.
"I remember so well when Tam was captured and the high hopes everyone had that he could be the founding member of a successful captive breeding program in Sabah, and join the then-international efforts involving the US and Indonesia," Susie Ellis, executive director of the International Rhino Foundation, said in a statement. "Sadly, those hopes were repeatedly dashed over the next decade by a series of incidents, some sociopolitical, some biological, and some simply bad luck."
Efforts to save the species in Malaysia have since focused on reproductive technology, including in vitro fertilization, but have so far proved unsuccessful.
Rhinos are under threat across the globe. The western black rhino, native to western Africa, was declared extinct in 2013. The last male northern white rhino died last year, bringing the species to the brink of extinction.