LOS ANGELES, United States - A grizzly bear attacked and killed an American man as he was cycling near the Glacier National Park in the northwestern state of Montana, the authorities said Thursday.

The bear attacked Brad Treat, 38, after he and a friend apparently disturbed the animal while mountain biking Wednesday afternoon, local officials said.

"It appears they likely surprised the bear and Treat was taken off his bike by the bear," the Flathead County Sheriff's office said in a statement. "He was pronounced dead on the scene."

The second rider was unharmed and managed to alert the authorities, the statement said, adding that the area has been closed off while officers search for the animal.

Grizzly bears were listed as a threatened species in 1975 in 48 US states. Northwest Montana is home to the largest grizzly population, with around 1,000 living in the region.

Attacks like Wednesday's are rare, officials say, and only 10 people have died in grizzly bear-related incidents in Glacier since the park opened in 1910.

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