JAY-Z and officials at his Roc Nation entertainment company have called on a top Wisconsin prosecutor to fire and charge a police officer accused of fatally shooting three people of colour in just five years.

The rap mogul and his team of social justice advocates took out a full-page advertisement in the Milwaukee Journal Sentinel on Thursday, directly addressing Milwaukee County District Attorney John Chisholm and urging him to take action against Wauwatosa officer Joseph Mensah, reports TMZ.

Mensah is accused of using excessive force in multiple incidents since joining the Wauwatosa Police Department in 2015, with three ending in the deaths of Alvin Cole, Antonio Gonzales, and Jay Anderson.

The open letter begins, "District Attorney Chisholm, Let us start off with a simple question - how many more people must die at the hands of Officer Joseph Mensah?"

It then claims Mensah fired a total of 19 shots during the clashes, stating, "His actions demonstrate an utter disregard for the lives of these young men."

"Outside of the three tragedies associated with Mensah, no other fatal shootings by police have taken place in Wauwatosa since Mensah joined the force in 2015. Doesn’t that tell you something?" the letter asks.

The Roc Nation representatives, together with officials from social justice organisations Until Freedom and The Gathering for Justice, go on to demand Chisholm 'immediately' fire Mensah and hold him "accountable for his actions and protect Wauwatosa citizens from further tragedy."