Celebrities appeal for calm after four police officers are shot dead in Dallas

At least two people opened fire on police officers during protests in Dallas on Thursday night killing five officers and injuring seven others.

Dallas Police Chief David Brown said the snipers fired "ambush style".

Police say in a statement that three people are in custody and authorities are negotiating with a suspect in a car park who has been exchanging gunfire with officials.

They said a suspicious package had also been secured by a bomb squad.

Celebrities appeal for calm after four police officers are shot dead in Dallas

Police say they're not certain that all the suspects have been located.

The protests were being held after the police shootings of black men in America this week.

On Tuesday a video emerged showing two white police officers holding down and shooting Alton Sterling in Louisiana.

The following day another video - which was live streamed on Facebook - claimed to show the aftermath of police shooting Philando Castile in his car in Minnesota.

It led to a debate about police brutality in the US

Celebrities in America have been reacting to the deaths of the four police officers in Dallas.