BANFF, Alberta (Reuters) - A Canadian woman who was killed by a cougar while skiing in scenic Banff National Park was stalked by the predator then attacked from behind in what park officials described Wednesday as an extremely rare event

In an incident that has shocked residents and tourists alike, the 30-year-old woman's body was discovered Tuesday afternoon by another cross-country skier on a trail a few kilometers east of the Rocky Mountain resort town of Banff, Alberta.

A healthy, 60 kilogram (130-pound) male cougar was found standing over the woman's dead body. Park wardens shot it immediately and launched an investigation into the attack, believed to be the first-ever killing of human by a cougar in Alberta.

Park officials said the incident, on a trail near picturesque Lake Minnewanka, may be a symptom of changing wildlife habitats in Banff, Canada's most famous skiing and hiking mecca.

"Through the backtracking it was apparent that the cougar hid behind a tree a distance from the trail,'' Ian Syme, Banff's chief park warden, told reporters on Wednesday. "The woman skied by on her way back to the trail head, the cougar bounded up behind and jumped on her back and killed her.''

Police have not released the victim's name.

The park, with its soaring mountain peaks and dense forests, is known for populations of predators such as cougars, wolves and bears, and prey like elk and mountain sheep.

Since the incident - and a series of sightings in and around the town of 6,500 on Tuesday, now believed to have involved a different cougar - park officials have been going door to door to warn residents and tourists and provide safety tips to avoid contact with the usually reclusive big cats.

"I'd like to stress that this cougar was exhibiting highly unusual behavior and that we may never know what caused this tragic attack,'' Syme said.

Cougars usually hunt at dawn or dusk, but the skier was killed in the early afternoon, he said. Even sightings of cougars are rare, and only four or five of the carnivores are believed to live near the town.

But early on Tuesday, another cougar attacked a dog that was in the backyard of a home in Banff. The dog was found alive on Wednesday and was being treated by a veterinarian.

A few hours later, a woman was walking her dog along a forested trail in town when a cougar approached her. She backed away and was not harmed. Later, wardens found an elk that had been killed by one of the predators.

A growing wolf pack to the west of town may be driving the cougars closer to the main hub of human activity to look for food, Syme said. "They are utilizing this space around the Banff townsite in a way that a wolf pack hasn't been utilizing it in the past,'' he  said. "The  wolves  and  the cougars