President Obama addressed last night's shooting in Dallas, where multiple snipers shot and killed five police officers, wounding six others, during a Black Lives Matter rally over the police shootings of Alton Sterling in Louisiana and Philando Castile in Minnesota.

"We still don't know all the facts," President Obama said at the beginning of a press conference in Warsaw, where a NATO summit is being held. "What we do know is that there has been a vicious, calculated and despicable attack on law enforcement."

"Police in Dallas were on duty doing their jobs keeping people safe during peaceful protests," the president said. "These law enforcement officers were targeted."

"I believe I speak for every single American when I say we are horrified by these events and stand united with the people and police department of Dallas," the president said he told the Dallas mayor.

The president said there were multiple suspects and that the country would "learn more about motivations" soon, although there was "no possible kind of justification for these kinds of attacks or any violence against law enforcement."

"I will have more to say about this as the facts become more clear," the president said while noting that even in his comments yesterday about the police shootings that precipitated protests in Dallas and around the country that police "had an extraordinary difficult job and the vast majority of them do their job in outstanding fashion."

"I also indicated the degree to which we need to be supportive of those officers that do their jobs each day," he said. "Today is a wrenching reminder of the sacrifices that they make for us."

"We also know that when people are armed with powerful weapons unfortunately it makes attacks like these more deadly and more tragic," he continued, "and in the days ahead we'll have to consider those realities as well."

Unless the snipers turn out to be former law enforcement officials or another special class with privileged access to weapons, in which case, as with the Orlando shooter who worked for a major Homeland Security contractor with all kinds of weapons clearance, the details won't matter. Earlier this year a police officer in Philadelphia was killed using a gun that had been previously stolen from the police department.

"But today our focus is on the victims and the families," Obama continued. "They are heartbroken. the whole city is grieving. Police around the country, a tight knit community, are grieving like a family." He asked Americans for "prayers as a nation" and to express "profound gratitude to our men and women in blue, not just today but every day."

The Dallas shooting was the deadliest event for law enforcement since 9/11, when 72 law enforcement officials died.

The Dallas downtown area is still reportedly being swept for suspects as well as bombs, which one of the suspects claimed had been planted.