'America is horrified,' says Obama after snipers kill 5 cops in Dallas

Dallas/Warsaw: US President Barack Obama on Friday denounced the "despicable" attacks in Dallas in which snipers shot dead five police officers during a protest against police shootings of black men.

"There has been a vicious, calculated and despicable attack on law enforcement," Obama said during a press conference at a NATO summit in Warsaw, adding that the officers were "targeted" by multiple suspects.

He said said America is "horrified" over the shootings and ensured justice would be done. He asked all Americans to pray for the fallen officers and their families.

Read: Video captures moments of chaos when snipers shot at police officers in Dallas

Police described Thursday night's ambush as carefully planned and executed and had taken three people into custody before a fourth died from what Dallas-based media said was a self-inflicted gunshot after a standoff that extended into Friday morning.

The fourth suspect had exchanged gunfire with police during the standoff at a downtown garage and warned of placing bombs throughout the city. Police have yet to confirm his death. But reports said that the fourth suspect committed suicide by shooting himself.

Read: Our worst nightmare has happened: Dallas Mayor after horrific shooting

The attack, which took place as a protest in Dallas was winding up under the watch of officers, was one of the worst mass shootings of police in U.S. history.

White House officials have spoken with Dallas Mayor Mike Rawlings about the shooting that turned the downtown of one of the largest U.S. cities into a sprawling crime scene, unfolding along streets that house major corporations, restaurants and government offices.

Read: Dallas shooting suspect dead after standoff, says media

Obama said the FBI was in contact with the Dallas Police Department and that the federal government would provide any assistance to Dallas as it deals with the incident.

"We still don't know all of the facts. What we do know is that there has been a vicious, calculated and despicable attack on law enforcement," he said.

No specific motive has been given for the shootings at the 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.

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, adding a civilian was also wounded.

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