A suspect who was killed after fatally shooting five police officers was "not affiliated" with any group, Dallas Police Chief David Brown has said. 

The incident took place on Thursday night during a peaceful Black Lives Matter protest against police killings of black Americans across the country.

The officers were shot by snipers from elevated positions, the Dallas Police Department said. 

Another seven officers and two civilians were wounded, according to the Dallas Morning News. 

Dallas, the third largest city in the US state of Texas, is home to an estimated 1.3 million people. 

"The suspect said he was upset about Black Lives Matter," Brown told reporters. "He said he was upset about the recent police shootings; the suspect said he was upset at white people.

"The suspect said he wanted to kill white people, especially white officers," he continued. "The suspect stated that we will eventually find the IEDs. The suspect stated he was not affiliated with any groups and he stated that he did this alone." 

The suspect exchanged fire with police officers and was then killed by police when they detonated an IED carried by a robot in the parking garage of the El Centro College in downtown Dallas. 

Brown said negotiations broke down and police "saw no other option but to use our bomb robot". He added that three other suspects are presently in police custody. 

Dallas Mayor Michael Rawlings urged people to join a prayer vigil for the officers who were killed at noon local time.

Heidi Zhou-Castro said it was "the worst attack on law enforcement officers in the United States" since the September 11 attacks in 2001.

"It is a different Dallas altogether this morning as people awoke to this tragic news," she told Al Jazeera from Dallas.

Country-wide protests
Speaking to Al Jazeera from Washington DC, Debbie Hines, a lawyer and former Baltimore city prosecutor said the "vigilantism is not going to solve any of the problems we have in the US".

"The divisiveness is caused by institutionalised racism in this country, and that's not an easy fix. But I think that on a simplistic level the police have to be retrained," she said.

"One thing we need to do is to get a hold of how pervasive the problem is and that would mean a national database of collections of how many officer-involved shootings and police brutality, as well as officer-involved deaths, that we presently don't have."

The protest in downtown Dallas was called after police killed two black men within 48 hours earlier this week - Alton Sterling in Louisiana on Tuesday and Philando Castile in Minnesota on Wednesday. 

Both the mayor and the police chief said the protest was peaceful. 

Several protests that took place across the country passed without incident.

Castile was shot dead by a police officer while he was in a car with his partner Diamond Reynolds and her daughter in a St Paul suburb. 

Reynolds live streamed the aftermath of the shooting in a widely shared Facebook video.

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

Of the 566 people killed by US police so far this year, The Guardian's database on police killings says at least 24 percent were Black.

African Americans comprise 13.3 percent of the country's population of 321million,according to the US Census Bureau. 

'Vicious, calculated and despicable' 
US President Barack Obama, addressing the media in Warsaw where he is attending a NATO summit, called the Dallas incident a "vicious, calculated and despicable attack" for which there was "no possible justification".

"We need to be supportive of those officers who do their job every single day. Today is a wrenching reminder of the sacrifices they make for us. When people are armed with powerful weapons, it makes attacks like these more deadly and more tragic."

A day earlier, responding to the recent killings of black men by police, he said that all Americans should be concerned about racial disparities in the criminal justice system.

"I also said yesterday our police have an extremely difficult job and that the vast majority are doing their job in outstanding fashion," Obama said.

'Everyone started running'

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

Carlos Harris, who lives downtown, told the newspaper that the gunmen "were strategic. It was tap tap pause. Tap tap pause."

Video footage from the scene showed protesters marching along a street in the city centre, about half a mile from City Hall, when the shots erupted and the crowd scattered, seeking cover.

Texas Governor Greg Abbott called for unity.

"In times like this we must remember - and emphasise - the importance of uniting as Americans," he said, in a statement.

The search stretched throughout downtown Dallas, an area of hotels, restaurants, businesses and some residential apartments. The scene was chaotic, with helicopters hovering overhead and officers with automatic rifles on street corners.

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.

Courtesy Aljazeera