Updated

Chimpanzees at a sanctuary for the animals in eastern South Africa pulled an American researcher who was leading a tour into their enclosure, bit him severely and dragged him nearly half a mile (kilometer).

The man was giving a lecture at the Jane Goodall Institute Chimpanzee Eden on Thursday when two chimpanzees grabbed his feet and pulled him under a fence into their enclosure, said Jeffrey Wicks of the Netcare911 emergency services company.

He was in intensive care in critical condition Friday after undergoing surgery at the Mediclinic hospital in Nelspruit, 180 miles (300 kilometers) from Johannesburg, hospital officials said.

The man had "multiple and severe bite wounds" and was dragged nearly half a mile (kilometer) by the chimpanzees, Wicks said.

Edwin Jay, chairman of the Jane Goodall Institute South Africa, said the man had crossed the first of two fences separating the chimpanzees from visitors and was standing close to the second fence, which is electrified, at the time of the attack.

Jay said the two chimpanzees involved were part of a group that had been rescued from Angola and brought to South Africa more than a decade ago. He said they were placed in their night enclosure and would be held there while sanctuary officials investigate what led to the attack and confirm the fencing is safe. Then they will be returned to the enclosure.

Jay would not release the man's name, saying only that he was an American researcher. Tourists visiting the sanctuary at the time were evacuated safely, he said.

The man lost part of an ear and parts of his fingers in the attack, according to the South African newspaper Beeld. It said the sanctuary's director fired into the air to scare the chimps away from the man, then chased them back into their enclosure.

The international institute founded by renowned primatologist Jane Goodall opened the sanctuary in 2006. It is a home to chimpanzees, which are not native to South Africa, rescued from further north in Africa. Some of the chimpanzees at the sanctuary lost their parents to poachers in countries where they are hunted for their meat, and others were held in captivity in cruel conditions.

In the United States, a Connecticut woman, Charla Nash, was attacked in 2009 by a friend's chimpanzee that ripped off her nose, lips, eyelids and hands before being killed by police. The woman was blinded and has had a face transplant. Lawyers for Nash filed papers this week accusing state officials of failing to seize the animal before the mauling despite a warning from a staff member that it was dangerous.