Andrew Oberle, the U.S. graduate student who was attacked by two chimpanzees while leading a tour at the Jane Goodall Sanctuary in South Africa, reportedly underwent six hours of surgery on Sunday and is recovering from his injuries.

The 26-year-old University of Texas grad student suffered extensive soft-tissue injuries to his arms and legs. However, officials at Mediclinic Nelspruit said that his wounds were cleaned and stitched while they induced sedation. He is in critical, but stable condition, MSNBC reported.  

Oberle was attacked on Thursday while leading a tour at the Jane Goodall Institute Chimpanzee Eden near Johannesburg. Oberle had been researching the chimps during for the summer while completing his degree.

During the lecture, Oberle reportedly walked into a restricted area of the sanctuary. ABC reported that Oberle picked up a rock that two chimps, Nikki and Amadeus, believed was part of their territory. One of the chimps dragged him under a second, electrified fence. The primates dragged the injured man along the ground for more than a mile as he tried to break free.

According to eyewitnesses, two chimpanzees grabbed the man by his feet and pulled him under the perimeter fence and into the enclosure, said Jeffrey Wicks, a representative of emergency service Netcare 911, Agence France-Presse reported.

This was the first time Oberle was asked to give a tour, the Daily News reported.

When paramedics arrived on the scene to help Oberle, they could not approach the enclosure. The animals were aggressive, and they were difficult to approach. They had to wait for armed guards before they could extract the victim.

The sanctuary instituted a lockdown and Eugene Cussons, the director at the Jane Goodall Institute Chimpanzee Eden, rushed to the scene.

Cussons drew a handgun and fired two rounds into the air and one round into the ground. However, the chimps were unfazed. In fact, they began to charge at Cussons. Nikki jumped on the hood of the car and began smashing the windshield.

Cussons said he fired a round through the glass and the chimpanzee calmed down and moved away. This allowed Cussons and the first responders to approach Oberle, reported ABC.

When we found him, he was in a fetal position underneath a lapa (a roofed, open-walled structure) with massive injuries, lacerations, abrasions, partial amputation from his head to toe, Lloyd Krause, a representative of the ER24 emergency service, was quoted as saying by AFP. He lost an ear, he lost a number of fingers and toes, he's got very deep wounds, he's got total removal of skin and muscle off his one leg and his one arm, fractures all over the place.

Oberle was reportedly experimenting with different food types. He wrote on his Facebook page that the mustard was a big hit.

David Oosthuizen, the executive director of the Jane Goodall Institute, commented on the situation.

This is a terrible tragedy that should never happen. All our thoughts and prayers are with this young man and his family, he said, reported to the Daily Mail. Any interaction between humans and wild animals can be dangerous, as wild animals are often very strong and can act aggressively if approached or if they feel threatened. Additionally, the chimpanzees at Chimp Eden have suffered horrible injuries and abuse from humans and therefore have to be treated with caution.

Oberle's friends and family have set up an account on We Pay in which well-wishers can contribute money for his medical needs.

We are asking people to donate anything they can, Anthony Reimherr, Oberle's roommate and friend, said statement, Andy is a fighter, he's made it this far, and I know he will not give up. We will not give up on him. In addition to monetary support, the Reimherrs are also asking that people send prayers and leave encouraging messages on the Facebook page.