The U.S. Marshals Service is investigating after a protester was badly injured this weekend at a demonstration outside the Portland federal courthouse, the city’s mayor said.

Ted Wheeler, the Democrat, announced on Twitter late Sunday that he spoke with U.S. Attorney Bill Williams and learned that the agency will be “conducting a full investigation.” He said the incident "should not have happened.

July 2: Officers with the Federal Protective Service can be seen, top right, holding their shields up and guarding the doorway of the Hatfield Federal Courthouse after the glass door shattered. (U.S. Attorney's Office District of Oregon via AP)

Oregon Public Broadcasting reported that the protester, Donavan LaBella, was struck in the head by what his friends described as an impact munition. Oregonlive reported that he suffered skull fractures and needed surgery.

Graphic video of the aftermath of the incident circulated online that showed a young man bleeding profusely from the mouth and nose, reports said. The 26-year-old’s mother told OPB that her son was out of surgery and responding to doctors.

“He’s had some facial reconstruction surgery,” she said. “They’re just watching him right now.”

The U.S. Marshals Service did not immediately respond to an after-hours email from Fox News seeking comment.

The intense protests in the city-- that have gotten violent-- have been taking place for more than a month and a half and city officials appear to be growing tired of the unrest and safety concerns.

“Portland continues to be used as a staging ground for violence night after night,” Wheeler tweeted. “This is causing unprecedented harm to our communities, livelihoods, and Portlanders continue to fear for their safety.  My main concern is this: that the continuing violence will lead to further injuries or even deaths.”

Williams said in a statement earlier this week that U.S. Marshals Service deputies and officers from the Federal Protective Service, Homeland Security Investigations and U.S. Customs and Border Protection have all been on duty protecting the courthouse.

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Protesters began targeting federal facilities in Portland on May 28, and the field office of the U.S. Immigration and Customs Enforcement “was targeted by a Molotov Cocktail,” the Associated Press reported.

The Associated Press contributed to this report