(CNN) A Sacramento County sheriff's deputy struck a protester with his patrol SUV as she and others gathered in the street to denounce the killing of Stephon Clark, then left the scene, according to video of the incident.

The incident Saturday night threatens to exacerbate an already tense relationship between police and protesters in California's capital. Observers say the deputy struck the woman at a high rate speed of speed, while authorities say the vehicle was moving slowly and the deputy was responding to a dangerous situation created by some of the demonstrators.

"This is their response to a community in outrage and pain; this is ​just ​another glaring example of the ​reckless nature of Sacramento law ​enforcement," said Tanya Faison, founder of Black Lives Matter's Sacramento chapter, which did not organize the event but has been vocal about Clark's killing.

"We will continue to demand justice for not just Stephon, but for all lives that have been unjustly taken at the hands of law enforcement."

During a vigil, a woman carrying a "Stephon Clark Rest in Power" sign walked in front of a sheriff's vehicle and motioned the driver to stop, according to a video from the National Lawyers Guild Legal Observers. The deputy then drove away, said Guy Danilowitz, a legal observer who recorded the video.

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