African-American residents in Baltimore are routinely subjected to unconstitutional stops, arrests and excessive force by the Baltimore Police Department, a scathing federal report released on Tuesday said.

The 163-page U.S. Justice Department report details an investigation launched after the death of black detainee Freddie Gray last year that found the Baltimore Police Department engages in a pattern of conduct that violates the constitution or federal law.

"This pattern or practice is driven by systemic deficiencies in BPD's policies, training, supervision and accountability structures that fail to equip officers with the tools they need to police effectively and within the bounds of the federal law," the report said.

However, the department "has already begun laying the foundation for reform by self-initiating changes to its policies, training, data management, and accountability systems", it added.

A spokesman said the department would not comment until a scheduled news conference on Wednesday.

The report comes 16 months after police arrested Gray, 25, for fleeing unprovoked in a high-crime area. He suffered a neck injury in a police wagon while shackled and handcuffed, and died a week later.

The incident triggered rioting and protests in Baltimore, a majority-black city of about 620,000 people. It fueled a national debate on police tactics and stoked the rise of the Black Lives Matter movement.

Six officers were charged in Gray's death, but four trials ended without a conviction. Prosecutors dropped the remaining charges last month.

The Justice Department's investigation after Gray's death found that the Baltimore Police Department had routinely made unconstitutional stops, searches and arrests.

"BPD's targeted policing of certain Baltimore neighborhoods with minimal oversight or accountability disproportionately harms African-American residents," the report added.

The investigation found African-American pedestrians were stopped three times as often as white residents after controlling for the population of the area in which the stops occurred, the report said.

Police have also engaged in a pattern of using excessive force when dealing with individuals with mental health disabilities, juveniles and subjects who do not immediately respond to verbal commands, the investigation found.

The department "uses overly aggressive tactics that unnecessarily escalate encounters, increase tensions, and lead to unnecessary force, and fails to de-escalate encounters when it would be reasonable to do so," the report said.

Police in Baltimore also have frequently violated the First Amendment of the U.S. Constitution by detaining and arresting individuals who engaged in protected speech, the report said.