The US is on a knife-edge this morning after a shocking night of violence that saw five police officers shot and killed in Dallas, Texas, during a protest march against the police shooting of two black men earlier this week.

Eleven officers were shot at by snipers in the city, and four died from their injuries in what police chiefs now believe to be a coordinated ambush. It was confirmed early on Friday morning (Irish time) that a fifth police officer had died from gunshot wounds. https://twitter.com/MSaavedraTV/status/751235837614927872 https://twitter.com/WhoAteMyPizza/status/751234410918219776 Dallas police chief David Brown said two shooters attacked from "elevated positions", with the plan to "injure and kill as many law enforcement officers as they could.” https://twitter.com/WesleyLowery/status/751258771309993984 https://twitter.com/dallasnewsphoto/status/751258609380564992 It's believed that police later cornered one suspect in a parking garage, where a shoot-out ensued for at least 45 minutes. The suspect reportedly told police negotiators that bombs had been placed in the vicinity, and a suspicious package was soon secured near the scene by Dallas bomb squad. https://twitter.com/cbs11doug/status/751234258006634496 Police also released an image of another suspect in the shooting, and the photo soon went viral. This man soon turned himself in, and he has since been released. https://twitter.com/DallasPD/status/751262719584575488 As it stands this morning, the other suspect remains in custody, but the investigation is ongoing. https://twitter.com/DallasPD/status/751271541459984384 The violence erupted during a protest march - one of many held across the US - in response to the deaths of two African-American men this week. Alton Sterling, 37, was confronted by officers for selling CDs outside a convenience store on Tuesday in Baton Rouge, Louisiana. Police have said they believed Sterling was carrying a gun, something which still hasn't been clarified in the days since. A struggle ensued, during which Sterling was shot dead.

via ABC Breaking News

Meanwhile, 32-year-old Philando Castile was shot dead on Wednesday after being pulled by police over for having a broken car light in Falcon Heights, Minnesota. His girlfriend, Diamond Reynolds, and young daughter were also in the car at the time. Reynolds live-streamed the aftermath of the incident on Facebook, in which she explains that Castile told the officer that he was carrying a firearm, and that as he reached for his requested licence and registration, the officer shot him. Their young daughter can be heard consoling her mother, saying: “It’s okay Mommy. I’m right here with you.” https://twitter.com/AlexontheMic/status/750925605797896192 The two black mens' deaths have convulsed the US once again in a debate and a row over race relations in the country. Minnesota Governor Mark Dayton said of Castile's death: “Would this have happened if the driver were white, if the passengers were white? I don’t think it would have.” #BlackLivesMatter protests and rallies have been staged in cities across the US in the days since. [caption id="attachment_301717" align="aligncenter" width="1024"]

Activists protest in Times Square, New York, in response to the recent fatal shootings of two black men by police (Yana Paskova/Getty Images)

  [/caption] https://twitter.com/serenawilliams/status/751074188786630657 Beyonce posted this message on her website last night: The star also held a moment's silence during her Glasgow show last night, against a background of the names of victims of police brutality. https://twitter.com/TheAussieSide/status/751161860607471616 https://twitter.com/Bey_Legion/status/751181915605110784 US president Barack Obama posted this message on his official Facebook page last night: It reads:

"All Americans should be deeply troubled by the fatal shootings of Alton Sterling in Baton Rouge, Louisiana and Philando Castile in Falcon Heights, Minnesota. 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. Although I am constrained in commenting on the particular facts of these cases, I am encouraged that the U.S. Department of Justice has opened a civil rights investigation in Baton Rouge, and I have full confidence in their professionalism and their ability to conduct a thoughtful, thorough, and fair inquiry. But regardless of the outcome of such investigations, what's clear is that these fatal shootings are not isolated incidents. They are symptomatic of the broader challenges within our criminal justice system, the racial disparities that appear across the system year after year, and the resulting lack of trust that exists between law enforcement and too many of the communities they serve. To admit we've got a serious problem in no way contradicts our respect and appreciation for the vast majority of police officers who put their lives on the line to protect us every single day. It is to say that, as a nation, we can and must do better to institute the best practices that reduce the appearance or reality of racial bias in law enforcement. That's why, two years ago, I set up a Task Force on 21st Century Policing that convened police officers, community leaders, and activists. Together, they came up with detailed recommendations on how to improve community policing. So even as officials continue to look into this week's tragic shootings, we also need communities to address the underlying fissures that lead to these incidents, and to implement those ideas that can make a difference. That's how we'll keep our communities safe. And that's how we can start restoring confidence that all people in this great nation are equal before the law. In the meantime, all Americans should recognize the anger, frustration, and grief that so many Americans are feeling -- feelings that are being expressed in peaceful protests and vigils. Michelle and I share those feelings. Rather than fall into a predictable pattern of division and political posturing, let's reflect on what we can do better. Let's come together as a nation, and keep faith with one another, in order to ensure a future where all of our children know that their lives matter."