Boston Police are investigating a report that officers assaulted a man.

A department spokesman said an investigation is underway after a person using the Twitter handle SaintSuave posted a bloody photo of himself with the message, "They said I looked suspicious so they beat my ass and sent me home. Thank You @bostonpolice. I thought I was safe here but apparently not."

An official complaint was filed Sunday, according to the spokesman. It was not clear when or where the alleged assault occurred, or which officers may have been involved.

Speaking during an interview with WBUR's Radio Boston, Mayor Marty Walsh confirmed an investigation was underway but said he didn't have any further details.

"It's certainly something that bothered me when I saw it, because it's not the conduct that I would expect from anyone who works for the city, particularly the police department," he said. "I was a little surprised when I saw the photo."