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Four DC Metro police officers were injured and 21 people were arrested when pro-Trump and anti-Trump groups clashed near the White House Saturday night.

An MPD spokesperson said the officers' injuries were non-life threatening. One officer was hit with an unknown chemical in the face and suffered vision problems. The PIO said the officer's vision does not appear to be permanently affected.

D.C. Police Chief Peter Newsham told the Washington Post people from both sides — and from outside and inside the region — came “intent on clashing,” and “the police department was put directly in the middle of it.”

Newsham said as opposing groups faced off, “police officers ran and placed themselves between them,” which he said he believed “prevented a much worse outcome.”

In all, police arrested 21 people, including one juvenile, on charges that include assault, disorderly conduct and inciting violence. Eight firearms were seized and five people were arrested on gun charges, including two Newsham said were linked to a Georgia-based armed group.

While multiple police lines kept the two sides apart, the nighttime clashes led to fistfights and at least one stabbing, Fox News reports.