President Barack Obama called the shootings in Dallas that left five police officers dead and several others wounded during a protest against police on Friday a “vicious, calculated and despicable attack on law enforcement.”

Obama, speaking from at a NATO summit in Poland, that America is “horrified” over the shootings and asked all Americans to pray for the fallen officers and their families. He also said the nation should express its gratitude to those serving in law enforcement.

Dallas Police Chief David Brown said earlier Friday that it was ”our assumption” that four suspects were working together with rifles, triangulating at different positions." He had no information on a possible motive or the identities of any of the suspects. He also noted that police were not completely certain that every suspect was in custody.

Gun battle with suspected sniper

 

Brown also said authorities had earlier taken a woman into custody near the garage. Two men were also being questioned after police pursued their vehicle away from downtown onto Interstate 35.

A fourth man was in an hours-long standoff with police. He was firing at officers and around 2:15 a.m. local time and told police “the end is coming.” He later died from a self-inflicted gunshot wound, according to KDFW-TV. Police were sweeping the area for possible explosives.

Late Thursday, Brown confirmed the four fatalities — three Dallas PD officers and one transit officer — and said seven other officers and one civilian were wounded in the shooting. Three of the injured officers reportedly were in critical condition and two others were in surgery. The Dallas Police Association confirmed a fifth officer had died in a Tweet early Friday.

DART identified its fallen officer as Brent Thompson, 43. He is the first DART officer to be killed in the line of duty.

Brown said multiple shooters positioned themselves in two parking garages in downtown Dallas and "planned to injure and kill as many law enforcement officers as they could."

A Dallas police source estimated to Fox News that at least 60 rounds were fired over a "large kill zone." The source added that the shooting would have required considerable planning.

"It's a heartbreaking moment for the city of Dallas," Mayor Mike Rawlings said. "I ask everybody focus on one thing right now, and that is Dallas police officers, their families, those that are deceased [and] those that are in the hospital fighting for their lives."

Fox4 cameras captured protesters running away from the scene of the shooting shortly before 9 p.m. local time. A cameraman approached the scene and captured officers apparently lying on the ground.

Aerial images showed officers appearing to focus their search on a nearby parking garage, which may have served as the snipers’ perch.

Witness Carlos Harris told the Dallas Morning News the gunfire was "strategic. It was tap-tap-pause. Tap-tap-pause."

Texas Gov. Greg Abbott released a statement saying he has directed the Texas Department of Public Safety director to offer "whatever assistance the City of Dallas needs at this time."

"In times like this we must remember -- and emphasize -- the importance of uniting as Americans," Abbott said.

The protesters had gathered after a Minnesota officer on Wednesday fatally shot Philando Castile while he was in a car with a woman and a child in a St. Paul suburb. The aftermath of the shooting was purportedly livestreamed in a widely shared Facebook video.

A day earlier, Alton Sterling was shot in Louisiana after being pinned to the pavement by two white officers. That, too, was captured on a cellphone video.

Michael Bautista told KDFW the protest march had been "very peaceful" before the shooting started.

Brittany Peete, a demonstrator, told the Associated Press she didn't hear the gunshots, but she "saw people rushing back toward me saying there was an active shooter."

Peete said she saw a woman trip and nearly get trampled as people ran to get to safety.

"Everyone just started running," Devante Odom, 21, told The Dallas Morning News. "We lost touch with two of our friends just trying to get out of there."

Other protests across the U.S. on Thursday were peaceful. In midtown Manhattan, protesters first gathered in Union Square Park where they chanted "The people united, never be divided!" and "What do we want? Justice. When do we want it? Now!" In Minnesota, where Castile was shot, hundreds of protesters marched in the rain from a vigil to the governor's official residence. Protesters also marched in Atlanta, Chicago and Philadelphia.

Fox News' Bret Baier and the Associated Press contributed to this report.