The National Park Service has opened an investigation into a woman who was caught on video approaching a grizzly bear in Yellowstone National Park to take a photograph earlier this month. 

In the video posted online, the unidentified woman is seen near the park's Roaring Mountain parking lot approaching a female bear with two cubs moments before the animal rushes toward her.

The woman, who appeared to calmly walk away after the incident, seemed to disregard a park rule prohibiting visitors from getting within 100 yards of bears. 

Darcie Addington, a park visitor who filmed the May 10 incident from her car, told USA Today the woman was warned not to get near the animal. 

"It was terrifying," she told the newspaper. 

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Park rangers are looking for the woman, who was described as White in her mid-30s with brown hair and wearing all black clothing. The agency warns visitors to never feed bears, while noting that all of Yellowstone is bear habitat. 

The park averages one bear attack annually. In 2011 and 2015, three people were killed by bears inside Yellowstone, the park reports.