People are sharing this image as a symbol of the horror in Dallas

At least two snipers opened fire on police officers during protests in Dallas on Thursday, killing five officers and injuring seven others.

The protests were over the recent fatal police shootings of two black men this week, Philando Castile and Alton Sterling.

People have been sharing one image in particular, captured by photographer Ting Shen for the Dallas Morning News, which encapsulates the tragedy.

The image shows a Dallas Area Rapid Transit police officer being comforted at the entrance to Baylor University Medical Center's emergency room, where some of the wounded officers were taken.

The Dallas Morning News has put the image on their front page.

The image has been reshared on Twitter, frequently cited as one of the most powerful photographs of the night.

Three suspects have been taken into custody while a fourth was being pursued by police, however reports are emerging on social media that he has been neutralised - this is awaiting official confirmation.

Dallas Police Chief David Brown said in a statement earlier on Friday:

We still don’t have a complete comfort level that we have all the suspects.

We will continue a rigorous search of downtown until we are satisfied that all suspects have been captured.

To follow live developments, visit the Independent's live blog.

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