Snipers in Dallas shot 11 police officers, killing 5 of them.Three people in custody and a fourth person reportedly died during a standoff.
It happened at protests over two fatal police shootings of black men.
President Obama said in a speech from Poland, where he's meeting with leaders of the European Union and attending a NATO summit that America is "horrified" over the shootings and that there is 'no possible justification'.
The group Black Lives Matter has also condemned the killings.