In a statement just after arriving at the summit just after midnight Warsaw time, and before the Dallas protests erupted into violence, Obama said all Americans should be troubled by the videotaped police shootings of African-American men in Louisiana and Minnesota this week.
U.S. president Barack Obama has called on European leaders to stand firm against Russia, Islamic State and other challenges facing North Atlantic Treaty Organisation - even as the United Kingdom is poised to exit from the European Union.
"It's something we'll follow closely and if it's something that merits a change in plan we'll let you know", Earnest added.
He said: "There has been a vicious, calculated and despicable attack on law enforcement".
The western military alliance is to send four battalions on a rotating basis, to be in place starting next year.
He said the FBI is in touch with Dallas authorities to help in the investigation. A visibly frustrated Obama urged Americans to push for local law enforcement reforms and said all Americans, regardless of race, should care about the treatment of blacks and Hispanics by police.
Standing alongside European Council President Donald Tusk and European Commission President Jean-Claude Juncker, Obama says governments must move more quickly to deliver economic priorities to their people. "That just means all lives matter".
As previously reported, two snipers shot 11 officers near Dealey Plaza on Thursday night.
"Today is a wrenching reminder of the sacrifices they make for us", Obama said of law enforcement officers.
In his initial comments on racial bias in policing, Obama proved to be grimly attuned to the potential for violence directed at police and criticism that the protesters were hostile toward law enforcement.
Obama emphasized another part of that message in the aftermath Friday.
At least five officers were killed after gunfire erupted during a protest against police brutality.
"We need to bolster the defence of our allies in central and eastern Europe, strengthen deterrence and boost our resilience against new threats, including cyber attacks", he said.
As the city and the nation wait for answers, the president asked that people keep the victims and their families in their thoughts and prayers.
Obama, who has been continuously notified of the devastating fatal shootings in Dallas while in Poland, said there could be not possible explanation for the attack. "They should meet with the Newtown families - some of whom Joe saw yesterday - whose children would now be finishing fifth grade - on why it is that we think our liberty requires these repeated tragedies", he went on to say. Canada and Germany have committed to furnishing core units for Latvia and Lithuania.