Updated

A lone woman wearing a sundress stands in the street, seemingly placid as police in body armor advance on her.

That image has swept through social media as a defining moment of protests over recent police killings of black men in Louisiana and Minnesota.

On Saturday, a few hundred protesters had gathered outside the Baton Rouge Police Department when police came out of their headquarters dressed in riot gear and accompanied by a military-style, armored vehicle.

The riot police were lined up, shields down, protecting their faces, with shields and batons in their hands. Their intent seemed to be to clear protesters from the highway in front of police headquarters.

The crowd of protesters was gathered on the grass and in a park near the highway.

As the crowd and an AP photographer and reporter watched, a young woman wearing a flowing black-and-white sundress came out of the crowd and took up a position facing the riot police.

The woman, whose identity has not been confirmed, stood alone with a cellphone in her hand and arms crossed. One of the officers told her that if she did not move off the road, she would be arrested.

When she gave no sign she would be moving, an officer said, "Arrest her," and a crack opened in the wall of riot police. Three officers came through.

As the woman stood motionless, two of the officers, clad all in black armor and moving swiftly in tandem, reached the woman, grabbed her by the arms and pulled her back behind the line of riot police.

She is one of nearly 200 demonstrators arrested since Friday who may yet face criminal charges, Baton Rouge police said.

Tensions have been rising since last week's killings of Alton Sterling in Baton Rouge and Philando Castile in Minnesota by white officers, and an attack on police by a black sniper in Dallas that killed five officers.