Dramatic photos of an undercover cop pointing a pistol at protesters in California on Wednesday are circling around the web.

In the photos, which were published by the New York Daily News, a plainclothes officer points a gun directly at a crowd of demonstrators in the Bay area who were protesting recent police shootings of unarmed black men.

According to a Reuters photographer who witnessed the incident, the police officer had been participating in the march and then drew his weapon after he and his partner were attacked. Shortly thereafter, about 20 uniformed officers arrived on the scene to detain one man.

"An officer outside the Oakland Police Department was assaulted, and an arrest was made," read a police statement about the incident.

A spokesman for the Oakland Police Department also said that the department had responded to a request for assistance "made by an outside agency."

Other witnesses tweeted firsthand accounts of the incident with the cop, who was later identified as an officer with the California Highway Patrol.

"Undercover cop pulls out gun, threatens crowd after protesters outed them #oaklandprotest," tweeted @e_baldi early Thursday morning.

"Tall 6-foot-8 undercover and shorter 5-foot-8 undercover with mask on were confronted in dark part of 27th Street. Tall cop pulled out baton. Tall cop quickly threw baton on ground and then pulled out gun, holding it sideways all gangster. Someone then clocked the masked cop. Masked undercover wasn't beaten badly as I first heard from witness further away, but hit straight in face and knocked down," wrote Twitter user @DaveID in a series of tweets.

About 150 people participated in the protest Wednesday night, which began as a peaceful demonstration at the University of California, Berkeley campus.

However, violence erupted after protesters moved into Oakland, and some people began breaking into stores. At one point, about 50 people broke windows at a T-Mobile store and a Chase bank, said a police statement. Looting also was reported in a downtown area populated with small businesses.

In addition, protesters shut down two subway stations in downtown Oakland for some time late on Wednesday, city officials said.

Since the weekend, a string of protests have been held in Oakland and Berkeley after it was announced that neither police officer would be indicted in the chokehold death of Eric Garner in New York or the shooting of Michael Brown in Ferguson, Missouri.

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