CHEYENNE, Wyo. - A grizzly bear killed a man who was hiking with his wife in Yellowstone National Park's backcountry after the couple apparently surprised the female bear and its cubs on Wednesday, park officials said.

It was the park's first fatal grizzly mauling since 1986, but the third in the Yellowstone region in just over a year amid ever-growing numbers of grizzlies and tourists roaming the same wild landscape of scalding-hot geysers and sweeping mountain vistas.

The Wednesday morning attack happened just two days after the peak weekend for tourism in the park all year, on a trail close to Canyon Village near the middle of Yellowstone.

Details were sketchy but park officials said the bear attacked to defend against a perceived threat. They said the wife of the 57-year-old victim called 911 on her cell phone and other hikers in the area responded to her cries for help.

Yellowstone spokesman Al Nash said the couple saw the bear twice on their hike. The first time, they continued hiking. The second time, the grizzly was running at them and the man told his wife to run.

The woman told park officials she didn't see the bear attack her husband. When the bear went for her, Nash said, she dropped to the ground. The grizzly lifted her off the ground by the day pack she was wearing then dropped her.

The woman may have had scrapes and bruises but didn't seek medical attention, Nash said. Authorities weren't prepared to identify the couple until the man's family could be notified, he said.

Park officials worked Wednesday to clear the area of people. All trails and backcountry campsites in the area were closed and a warning sign was posted on the trailhead, Nash said.

"It is in the backcountry of the park, and we have access challenges and limited communication," Nash said.

The bears remained at large.

Grizzlies in the Yellowstone region have caused growing problems for people, everything from raiding bird feeders at rural homesteads to the very worst.

In June 2010, a grizzly just released after being trapped and tranquilized for study killed an Illinois man hiking outside Yellowstone's east gate. Last July, a grizzly killed a Michigan man and injured two others in a nighttime campground rampage near Cooke City, Mont., northeast of the park.

Yellowstone and nearby surrounding areas are home at least 600 grizzlies and some say more than 1,000. Once rare to behold, grizzlies have become an almost routine cause of curious tourists lining up at Yellowstone's roadsides at the height of summer season.

Meanwhile, those tourists have been flooding into Yellowstone in record numbers: 3.6 million last year, up 10 percent from 2009's 3.3 million, also a record.

The spokesman for the Wyoming Travel and Tourism state agency doubted the attack would cause anybody to change their Yellowstone vacation plans.

"What has happened here hasn't happened for a quarter century," Chuck Coon said. "It is very sad, though, and I'm very sorry to hear of it."

The big bears require constant vigilance for tourists and park employees alike, said Caleb Platt, a service station manager at Canyon Village who said he has had a handful fairly close encounters with grizzlies while hiking in the park.

"When it's close and you realize it does see you, it gets the heart racing," he told The Associated Press by phone.

He said he hadn't heard about the mauling near his workplace but carries bear spray - pressurized hot-pepper residue in a can - so he's able to defend himself in case a bear gets too close to him on the trail.

Park officials Wednesday issued a number of recommendations for park visitors to stay safe from backcountry bears. They included staying on designated trails, hiking in groups of three or more people, keeping alert for bears and making noise in places where a grizzly could be lurking out of sight nearby.

Bear spray is effective in stopping aggressive bears, they said.