Olivia Wilde shares her sadness after four police officers are assassinated

Olivia Wilde has led the celebrities expressing their sadness after four police officers were shot and killed on Thursday night (07Jul16).

The officers were working at a Black Lives Matter protest in Dallas, Texas, which was being held following the shootings of Alton Sterling and Philando Castile by police earlier this week. The initially peaceful protest turned violent when snipers opened fire on officers in the crowd, killing four and injuring several more.

Dallas Police Department's Chief Brown said that it was "two snipers" who committed the shootings, adding that the shooters "were positioning themselves in a way to triangulate on these officers from two different perches in the downtown area and planned to injure and kill as many law enforcement officers as they could."

One suspect is now in custody following a shootout with police, while officers are believed to be negotiating with the second man, who is currently holed up in a building.

As the situation unfolded, countless celebrities took to their social media pages to ponder the state of the world following the horrific shootings this week.

Olivia wrote on Twitter: "It is truly tragic when a vicious few turn a peaceful protest into a bloodbath. Horrific and sad. #nomoreviolence."

John Legend has been very vocal about his feelings surrounding the earlier shootings of Sterling and Castile, but insisted taking anger out on police in this way is completely "counterproductive".

"These Dallas shootings are horrific. Killing these officers is morally reprehensible and completely counterproductive to keeping us safe," he tweeted.

"Being against cops killing is not equal to being for killing cops. We need peace in our streets."

Demi Lovato tweeted, "#PrayingForDallas #PrayingForPeace. My heart hurts. God help us", while actor Don Cheadle added, "Sick, misguided mfs (motherf**kers) all around!"

Frozen star Josh Gad also eloquently expressed his views, writing: "There is tragedy. We answer it with tragedy. We demand justice. We seek vengeance. We hang our heads in sorrow. Sad week in the US of A."

Ariana Grande's brother Frankie tweeted: "OMG (oh my God) CAN WE ALL PLEASE STOP SHOOTING EACH OTHER!?!?!?!?!?

"I'm sobbing in bed right now! How can we possibly still live in such a horrible violent world? How can this actually be humanity!?!?"

Hamilton star Lin-Manuel Miranda also commented, though didn't directly refer to the shootings in his message, writing: "Those who hate us and fear us cannot bring us down. *looks around.* I love you. Good night."