A mobile phone app to help citizens record interactions with police was announced Friday by the ACLU of Minnesota in an effort, advocates said, to hold law enforcement officers more accountable.

The free Mobile Justice MN app allows users to record cellphone videos of exchanges with police when they feel their rights may be violated, and then automatically send the videos to the local ACLU office for review.

"This provides a different perspective. … This puts the power into the hands of individuals," said Teresa Nelson, legal director of the Minnesota ACLU, at a news conference in St. Paul.

The app arrives at a time when police locally and across the country have come under scrutiny owing to citizen recordings of arrests and other interactions. The heads of the Minneapolis and St. Paul police unions issued statements saying the new app could put the public at risk and interfere with investigations.

The app, for Android and iOS phones, was simultaneously launched in 10 other states and in Washington, D.C. It was already available in eight other states, where it has been downloaded about 250,000 times.

"The concerns over police practices, including racial profiling and excessive use of force, are very real for communities across the state," said Charles Samuelson, executive director of the Minnesota ACLU, in a statement. "This app will help serve as a check on abuse."

The Mobile Justice MN app allows exchanges to be sent straight to the ACLU once they're finished, a fail-safe in case the phone is taken from the person recording the event, Nelson said. The app also allows the user to file an incident report with the ACLU, and it offers a feature that summarizes the rights citizens have when stopped by officers.

The app's most controversial feature is its ability to let a user notify others when a police event is being recorded, so that they can go to the scene and observe what's happening.

Police union heads said the witness-alert feature could prove to be dangerous.

"It will almost certainly create public safety issues," said St. Paul Police Federation President David Titus, in a statement. "Encouraging people to flock to an unsecure and possibly dangerous police incident is not responsible or logical. … The ACLU app may require a larger police presence to de-escalate some situations, an outcome neither law enforcement nor the community desire."

Police Officers Federation of Minneapolis President Bob Kroll agreed.

"The ACLU in effect is dispatching unknown citizens to crime scenes to record not only officers but also victims, witnesses and even suspects," Kroll said in a release. "Cops could be in the early stages of an investigation of a child rape, domestic assault or a hate crime with unknown citizens, who were sent by the ACLU, capturing images of victims.

"Some victims or witnesses may shut down and not cooperate due to ACLU recordings for fear of further victimization or concern about their identities being posted all over social media."

Nicole Norfleet • 612-673-4495

Twitter: @nicolenorfleet