PHOENIX — A police officer in northern Arizona has been placed on administrative leave after a video posted to social media showed him punching a woman in the face before arresting her.

Flagstaff police said in a statement the department was investigating officer Jeff Bonar’s actions. “Our agency is very concerned by what is depicted in this video,” the release said.

In a press conference, Flagstaff Police Chief Kevin Treadway said Bonar was helping the Coconino County Sheriff’s Office with an eviction when he recognized the woman, Marissa Morris.

Treadway said Bonar was involved with a call related to Morris in October and believed she still had outstanding warrants. He wanted to detain her to check and the situation became heated.

“After her arrest, it was determined that the warrants had already been served and were no longer valid,” Treadway said.

Bonar, who was with another officer, and Morris, whom authorities described as “somewhat uncooperative,” had exchanged words before he hit her. Treadway said Bonar reported Morris had kicked and kneed him prior to the punch.

Morris was charged with aggravated assault and resisting arrest.

A witness posted the video to Facebook.

Police saw the video, which went viral, Wednesday evening, hours after the arrest. Treadway said police were unaware of the incident right away because Bonar went to the doctor to be treated for a respiratory illness.

Bonar was wearing a body camera at the time. Treadway said the footage would be released through public information requests.

Treadway said Bonar, who has been with the department for nearly three years, has no prior incidents.

Treadway said he asked the Northern Arizona University Police Department to conduct a separate criminal investigation into the incident.

The Associated Press contributed to this report.

Follow @KTAR923