At least one sniper opened fire on police during a protest in Dallas on Thursday night, killing four police officers and a transit officer during a protest rally against police brutality.

Police said seven police officers and two civilians had also been wounded.

The attack came amid protests across the country against police brutality, after two videos emerged this week of police killing two black men in Minnesota and Louisiana

Dallas Police Department (DPD) Chief David Brown said Friday that the gunman, who barricaded himself in a downtown garage, had been killed. Authorities later identified the man as 25-year-old Micah Johnson who was a member of the US army reserve.

Police used a robot bomb to detonate and kill Johnson after several hours of shooting and negotiations, he said, adding the decision to use the bomb was taken to avoid endangering officers' lives.

The assailant - holed up in the garage - had told police that there were bombs strewn throughout the garage and other places in downtown, Brown said.

Bomb squads later swept the area and did not find any explosives.

Brown said the gunman told negotiators he was upset over police killings of black people and wanted to kill white people, especially white police officers. Johnson reportedly added that he was not affiliated with any group and acted alone.

Police are still investigating possible additional suspects.

Five officers dead

Late Thursday evening, the police chief said in a statement that two snipers fired on a number of officers as the protest progressed through downtown Dallas.

"Three officers are deceased, two are in surgery and three are in critical condition," Brown said.

Police later confirmed two others had been killed, bringing the total death toll to five. Dallas Mayor Mike Rawlings told US broadcaster CBS that the assailants shot a total of 12 officers and two civilians.

A man carrying an assault rifle during the protest was wanted for questioning. "The person of interest whose picture has been circulated just turned himself in," Dallas police said in a statement.

However, the man told local news that he was mistakenly identified as a suspect, adding that he was legally carrying a firearm. Texas is an open-carry state, which allows individuals to carry certain guns as long as they are visible. He was later released by police, according to local media.

Police question suspects

Police had earlier said they took two of the suspects into custody in a traffic stop when an officer witnessed a person leave the scene of the shooting with a suspicious bag.

"A DPD officer observed an individual carrying a camouflaged bag, walking quickly down Lamar St. The individual threw the bag in the back of a black Mercedes and the Mercedes sped off at a high rate of speed," the police department said.

"Another alleged suspect was in a shootout with Dallas SWAT officers. That suspect is also in custody. A suspicious package was discovered near this suspect's location. The package is being secured by DPD bomb squad," the statement added.

Texas Governor Greg Abbott said he had directed the head of the state's Department of Public Safety to offer "whatever assistance the city of Dallas needs at this time."

The Dallas shooting comes amid planned rallies in several US cities after two black men were shot dead by police officers in Minnesota and Louisiana this week.

Philando Castile, 32, was shot during a traffic stop near Minneapolis, Minnesota, on Wednesday. One day earlier, police gunned down 37-year-old Alton Sterling outside a shop in Baton Rouge, Louisiana.

Obama comments

In Warsaw for a NATO summit, US President Barack Obama said he has been informed about the situation in Dallas and that the federal government will provide assistance to local authorities.

"There is no possible justification for these kinds of attacks or any kind of violence against law enforcement … Justice will be done," Obama said.

"When people are armed with powerful weapons, it makes attacks like this more deadly," he added.

ls/cw/nm/sms (Reuters, AP, AFP)