At least five police officers were killed and six others were wounded by snipers during a protest in Dallas on Thursday night.
The shooting came as a rally protesting the police shootings of black men in Minnesota and Louisiana earlier this week wound down. According to local media, gunshots rang out downtown at about 9 p.m. local time.
"Gunfights like the wild, wild West. Police officers started shooting in one direction. They don't know where they're shooting, but they start shooting, and whoever was shooting started shooting back," one witness told KXAS.
It was the greatest loss of life of law enforcement personnel since the Sept. 11 terror attacks in 2001, where 72 officers lost their lives.
President Barack Obama, who is in Poland for his last NATO Summit, called a special press conference to address the attack.
"I believe I speak for every single American when I say that we are horrified over these events and that we stand united with the people and the police department in Dallas," Obama said.
Dallas police say they believe at least four suspects coordinated the attack and positioned themselves near the end of the protest's route.
As of early Friday morning, police said they have three suspects in custody. Officials told local media a fourth suspect died after a standoff with police.