Five police men were killed by a sniper during a protest in Dallas against the killings of two black men by the Police on Thursday.
The protests were sparked by the deaths of Philando Castile in Minnesota and Alton Sterling in Louisiana.
In total, police say 11 officers were shot “ambush style” by snipers, killing three immediately.
A fourth officer died later.
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 that a fifth officer has died,” Dallas police said on Twitter.
No motive has been given for the ambush at a downtown protest, one of many held in major cities across the United States on Thursday.
New York police made more than a dozen arrests on Thursday night, while protesters briefly shut down one of Chicago’s main arteries.
Reports say one suspect is in custody after a shootout with the police, while a person of interest turned himself in.
The suspect in the standoff told the police “the end is coming” and that more police were going to be hurt and killed.
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 coordinated 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.
Brown said the suspect also told the police “there are bombs all over the place in this garage and downtown.”
“This suspect we are negotiating with for the last 45 minutes has been exchanging with us and has not been very cooperative with the negotiations,” Brown said.
Police said they were questioning two occupants of a Mercedes they had pulled over after the vehicle sped off on a downtown street with a man who threw a camouflaged bag inside the back of the car.
A woman was also taken into custody near the garage where the standoff was taking place.
“We are being very careful in our tactics so that we do not injure any of our officers or put them in harm’s way.
“We still don’t have a complete comfort level that we have all the suspects.
“We are leaving every motive on the table on why this happened and how this happened,” Brown said.
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 7 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.