Obama said he'd conveyed condolences to Dallas' mayor, and indicated the Federal Bureau of Investigation was involved in investigating the shootings, which left 5 police officers dead.
"It is my understanding that investigators have now publicly ruled out the possibility that the individual who carried out this awful act of violence had any sort of connections to terrorist organisations, either in the United States or around the world", White House spokesman Josh Earnest told reporters in Warsaw.
President Barack Obama and leaders from the 27 other North Atlantic Treaty Organisation member states are attending the summit, as well as leaders from the United Nations, European Union and World Bank, among others.
Obama had been scheduled to return to Washington on Monday.
Obama is slated to leave Poland on Saturday evening for his first presidential trip to Spain.
"He didn't get a lot of sleep last night and he won't get much tonight".
"The president has been updated on the shooting of police officers in Dallas", White House Press Secretary Josh Earnest said in a statement Friday morning. He has acknowledged becoming out of the touch with the public mood during past foreign travels and seemed determined not to let that happen this week.
"Even as yesterday I spoke about our need to be concerned as all Americans about racial disparities in our justice system, I also said yesterday that our police have an extraordinarily, hard job and the vast majority of them do their job in outstanding fashion".
The alliance has mounted a series of exercises, especially in the eastern member states, to test readiness levels and reassure nervous allies, and it has also deployed extra aircraft to boost air policing, especially over the Baltic states.
"When people say 'black lives matter, ' that doesn't mean blue lives don't matter", Obama said, referring to uniformed officers.
"We've seen such tragedies far too many times, and our hearts go out to the families and communities who've suffered such a painful loss", Obama wrote in a message posted to his Facebook account. "But right now, the data shows that black folks are more vulnerable to these kinds of incidents".
Obama expressed his gratitude to police officers and noted he had grieved with families of fallen officers. "Today is a wrenching reminder of the sacrifices they make for us", he said.
Obama said he spoke with Dallas Mayor Mike Rawlings early Friday and offered his support and condolences. The attacks in Dallas took place during a protest rally over the police shootings in other cities, which have prompted a national outcry and reignited debate over race and law enforcement. We are grieving with them.
A family member says a protester who was shot when snipers opened fire on police at a rally in Dallas was shielding her sons when she was injured.