Photographer captures stunning moment when undercover cop pulls gun on Oakland protesters

Police in Oakland, California, said demonstrators broke windows and looted stores and that one person was arrested for allegedly assaulting an officer in the latest protest of police activity in the United States.

Oakland and neighboring Berkeley have seen nightly demonstrations since the weekend in response to decisions by two grand juries not to charge white police officers in the killings of unarmed black men in Ferguson, Missouri, and New York City.

On Wednesday night, about 150 protesters - a smaller crowd than on previous evenings - left the campus of University of California-Berkeley and demonstrated without incident before marching south into Oakland, the city of Oakland said in a statement.

By that point, the protesters' numbers had dwindled to about 50 people, the statement said, some of whom broke windows at a T-Mobile store and a Chase bank. Looting also was reported in an area of small businesses at a downtown intersection, it said.

"An officer outside the Oakland Police Department was assaulted and an arrest was made," the statement said.

A Reuters photographer witnessed an undercover police officer, who had been marching with the demonstrators, pointing his pistol at protesters after he and his partner were attacked.

Two subway stations in downtown Oakland were shut down for a time because of the protest, city officials said.

On previous evenings this week in the Bay Area, riot police have fired tear gas and pepper spray to disperse demonstrators, some of whom have thrown stones at the officers.

The protests are part of nationwide actions by activists amid turmoil over the policing of black communities.

(Reporting by Emmett Berg; Editing by Daniel Wallis and Bill Trott)