José, who was killed last week, seen in his more recent home of Emoya Big Cat Sanctuary in South Africa. We're not crying. You're crying. Animal Defenders International/YouTube

Years of incredible conservation work has taken a knock back after a shocking attack on two former circus lions.

Animal Defenders International (ADI) has announced the “devastating news” that two lions they rescued from a circus have been poisoned and their bodies mutilated at a sanctuary in South Africa.

The two male lions, named José and Liso, were killed late last week at the Emoya Big Cat Sanctuary in Vaalwater, in northern South Africa’s Limpopo Province. The lions were discovered with their heads decapitated and their paws cut off.

"Our veterinarian conducted the autopsy and confirmed José and Liso ingested a huge amount of poison and died very quickly – they were not skinned alive as some media has suggested," ADI confirmed in a Facebook post.

“We have 24-hour security and armed patrols and have taken immediate, added measures to safeguard our big cats and sanctuary. There has been a steady stream of investigators and forensic experts through the sanctuary,” Emoya Big Cat Sanctuary said in a separate Facebook post.

The lions were rescued from a circus in Peru in 2015 after the Peruvian and Colombian governments introduced new laws prohibiting wild animals in circuses. They were flown to South Africa by ADI the following year. The ADI's Operation Spirit Of Freedom rescued over 100 animals, including 33 African lions. Most had their claws removed so it was not possible to return them to the wild. José had also been suffering head trauma and brain damage “likely caused by beatings in the circus.”

The motive for the lions' mutilation is not yet known, although the parts removed suggest the killings were for trophies, "traditional medicine", or ritualistic purposes. It’s now been investigating by police and specialized anti-poaching units.

Earlier this year, there were similar reports when three lions were also found with their heads and paws chopped off in Limpopo Province. In this particular instance, police said the animal parts were obtained on commission from traditional healers in the neighboring country of Mozambique.

There's a very real possibility ions could go extinct by 2050 if current poaching trends continue. The African Lion (Panthera leo) is currently listed as "vulnerable" on the IUCN Red List of Threatened Species. Although some subpopulations have increased in the south of Africa, lions can no longer be found in much of their historic range and the total population dropped by 43 percent between 1993 and 2014.

Among the many number of causes behind this drop is habitat loss, prey base depletion, and illegal poaching, which is largely fuelled by trophy hunting, the bushmeat trade, and the use of lion body parts in traditional medicine.