Five policemen were killed and six were wounded in Dallas, United States, on Thursday night after a protest rally against two African American men being fatally shot by two police officers in Minnesota and Louisiana turned violent. According to local news channels, this is the single-largest attack on law enforcement authorities in the United States. Dallas Police Chief David Brown said snipers shot 11 policemen from "elevated positions" during the demonstration at Belo Garden Park, CNN reported.

Three suspects are believed to be in custody, while another was killed in the ensuing violence. Police said one of the suspects told them he wanted to shoot white people, especially police officers. Dallas Police also said suspects threatened to plant a bomb in the city, and that the Federal Bureau of Investigation was asked to provide assistance in the case. Aviation authorities have restricted flights over the city after the shooting.

President Barack Obama, reacting to the incidents from Warsaw, Poland, called the shootings "a vicious, calculated and despicable attack on our [the US] law enforcement." He added that there is no justification for these kind of attacks.

On Tuesday, 37-year-old Alton Sterling was shot dead by Baton Rouge Police in the US state of Louisiana. Federal investigators are now looking into the incident, which surfaced after a graphic video of it was shared widely on social media. In the clip, policemen can be seen on top of Sterling before two shots are heard.

A day after Sterling’s shooting, police gunned down 32-year-old cafeteria supervisor Philando Castile during a routine traffic stop. His girlfriend, who streamed the aftermath of the incident live on Facebook, said Castile was reaching for his driver’s licence when the policeman fired, The Telegraph reported.

Both incidents triggered a nationwide outcry. Calling them tragedies, Obama said African Americans were more vulnerable to such attacks. The President, who is attending a NATO summit in the European country, quoted figures that proved minorities were more likely to be targeted by law enforcement, and emphasised on the need for such prejudices to be “rooted out”.