UPDATED 10.04PM The suspect in the killing of five Dallas police officers has died after during a stand-off in a parking garage, local channel NBCDFW reports.

It was first reported that the suspect had been shot dead by police, but that was later called into doubt.

At the moment it is not known whether the suspect was shot dead by the police or he died from a self-inflicted gunshot wound.

The deceased was one of the alleged perpetrators of the attack on Thursday night in Dallas, Texas, on a peaceful Black Lives Matter rally against police violence.

Six police officers were wounded as was a civilian.

The suspect barricaded himself in a parking lot and continued to exchange gunfire with police officers during negotiations, and said "the end is coming".

He had vowed to hurt and kill more police. He also said he had placed several bombs in the parking lot and in other parts of downtown Dallas.

Apart from the deceased, three other suspects are being held in police custody, including a woman who was arrested near the garage and two others who were travelling in a Mercedes car.

According to NBCDFW, a large area of downtown Dallas is in lockdown and police are investigating two suspicious packages.

Two separate bomb disposal squads were deployed to the premises where the suspicious packages were found, according to the local TV channel.

SEE ALSO: Another black man shot by police in the US

United States President Barack Obama said the FBI is working with Dallas law enforcement to investigate the shooting.

"Today is a wrenching reminder of the sacrifices [law enforcement] make for us," he said.

Obama also said the availability of automatic and high-powered weapons makes these attacks more likely and there would be talks on the subject in the coming days.

No motive has been given for the ambush at the downtown protest, one of many held in major cities across the United States.

Dallas Police Chief David Brown said the shooters, some in elevated positions, used sniper rifles to fire at the officers in what appeared to be a co-ordinated attack.

"(They were) working together with rifles, triangulating at elevated positions in different points in the downtown area where the march ended up going," Brown told a news conference.

It has been a devastating night. We are sad to report a fifth officer has died.

— Dallas Police Depart (@DallasPD) July 8, 2016

Police initially said four officers had been killed but the main union for Dallas police later reported that one of seven wounded officers had later died, taking the death toll to five.

"It has been a devastating night. We are sad to report a fifth officer has died," Dallas police said on Twitter.

One of the slain police officers has been named as 43-year-old Brent Thompson.

LISTEN: Dallas Morning News reporter Hannah Wise joins Larry Williams from the scene

The shooting happened as otherwise largely peaceful protests unfolded around the US after the shooting of Philando Castile, 32, by police near St Paul, Minnesota, late on Wednesday and Alton Sterling, 37, in Baton Rouge, Louisiana.

New York police made more than a dozen arrests on Thursday, while protesters briefly shut down one of Chicago's main arteries.

I am so scared. pic.twitter.com/jw88QnKGXG

— Allison (@allisongriz) July 8, 2016

A large area of downtown Dallas was an active crime scene, Dallas Mayor Mike Rawlings said.

"Our worst nightmare has happened, he said. "It is a heartbreaking moment for the city of Dallas." The Texan city is home to more than seven million people.

Rawlings later visited the wounded at Parkland hospital, the same hospital where President John F. Kennedy was taken after he was shot in Dallas in November 1963.

Television footage showed a heavy police presence, with officers taking cover behind vehicles on the street.

The use of force by police against African-Americans in cities from Ferguson, Missouri, to Baltimore and New York has sparked periodic and sometimes violent protests in the past two years and has spawned the Black Lives Matter movement.

Anger has intensified when the officers involved in such incidents have been acquitted in trials or not charged at all.