Five officers were killed and another 12 injured in a shooting in Dallas last night during a peaceful protest that was organised in response of the tragic deaths of Alton Sterling in Louisiana and Philando Castile in Minnesota.
The US Attorney General Loretta Lynch said an FBI investigation will be launched into the Dallas killing.
The US Department of Justice has opened a civil rights investigation in Louisiana and is providing assistance to local authorities in Minnesota who are leading the investigation there, she said.
"Rather, the answer must be action: calm, peaceful, collaborative and determined action. We must continue working to build trust between communities and law enforcement. We must continue working to guarantee every person in this country equal justice under the," the Attorney General said.
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US President Barack Obama said America is horrified over these killings.
"We stand united with the people and the police department in Dallas," he said at Warsaw where he is meeting with NATO and European Union leaders.
Taking the podium on the floor of the US House of Representatives, Speaker Paul Ryan said he is stunned by the events last night in Dallas.
"We are all outraged. An attack on the people who protect us is an attack on all of us," he said.
"There will be a temptation to let our anger harden our divisions. Let's not let that happen. There's going to be a temptation to let our anger send us further into our corners. Let's not let that happen. That script is just easy to write-it's too predictable. Let's defy those predictions," he said.
"I'm horrified by the murder of five law enforcement officials in Dallas and the wounding of many other officers and innocent civilians," said Senator John McCain.
Leaders of the Hindu American Foundation (HAF) joined millions across the nation in expressing horror and grief at the deliberate killing of five Dallas police officers and the wounding of 12 officers and two civilians.