Twelve police officers were shot by three snipers Thursday night during a Black Lives Matter rally — and five of those officers have died.

One sniper took his own life, and several others are in custody, according to multiple news reports. Details are continuing to emerge.

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It is the most brazen and deadly attack on law enforcement in this country since Sept. 11, 2001.

President Obama called it a “vicious” and “calculated” attack — and almost immediately blamed the attacks on guns and weapons.

“We’ve got to support our police force and [let] them do their job, and to make sure that we get to the bottom and the root cause of all this,” said Dallas Mayor Mike Rawlings early Friday morning. “It is a heartbreaking morning.”

Law enforcement veterans told Fox News that the attack was clearly coordinated and showed an alarming degree of planning and sophistication.

Here are earlier details as they became known last night during what Rawlings called “our worst nightmare.”

On Thursday night, the Dallas Area Rapid Transit confirmed via Twitter that four of their “police officers were shot in downtown Dallas” — one of them fatally. Other reports indicated that as many as 10 police officers had been shot by two snipers, with a total of three officers fatally injured.

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An unknown gunman opened fire on police officers at the scene of a reportedly peaceful Black Lives Matter protest, Fox affiliate KDFW in Dallas, Texas, reported.

Following the potentially questionable shooting deaths of two black men at the hands of police officers in a 48-hour time span, large protests were sparked in several major cities, including Dallas. Several major thoroughfares in New York City were shut down by large crowds of protesters Thursday evening.

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The first round of shots fired drew a massive police response in downtown Dallas, with the focus centered on a parking garage.

Several eyewitnesses on the ground, including a uniformed police officer, told KDFW the shooting suspect was armed with a rifle.