The president of one of the largest police organisations in the US has apologised for historical mistreatment of minorities, calling it a "dark side of our shared history" that must be acknowledged and overcome.

Terrence Cunningham, president of the International Association of Chiefs of Police, said at the group's annual conference on Monday that police have historically been a face of oppression, enforcing laws that ensured legalised discrimination and denial of basic rights.

He was not more specific.

San Diego police came under harsh criticism after officers there shot and killed an unarmed, metally ill man outside a shopping centre in September.

Cunningham said today's officers are not to blame for past injustices. He did not speak in detail about modern policing, but said events over the past several years have undermined public trust.

His comments come as police shootings of black men have roiled communities in Ferguson, Missouri; Baton Rouge, Louisiana; and suburban St Paul, Minnesota; and as black shooters have targeted officers in Dallas, the St Louis suburb of Ballwin and Baton Rouge.

"While we obviously cannot change the past, it is clear that we must change the future," Cunningham said.

"We must forge a path that allows us to move beyond our history and identify common solutions to better protect our communities.

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"For our part, the first step in this process is for law enforcement and the (International Association of Chiefs of Police) to acknowledge and apologise for the actions of the past and the role that our profession has played in society's historical mistreatment of communities of colour," he said.

Cunningham received a standing ovation for his remarks from thousands of law enforcement officials before he introduced Loretta Lynch, US attorney general, who largely avoided the topic.

He has been police chief since 1999 in his hometown of Wellesley, Massachusetts, an affluent, overwhelmingly white, low-crime suburb near Boston.

He served three years as vice president of the police chiefs association before becoming president in 2015 for a one-year term.

Apology falls short

David Alexander III, police chief in Pensacola, Florida, said recognising historical injustices is key to addressing race relations, just as acknowledging domestic violence was a step forward.

"When you don't know the history and you say, 'Well, there is no problem,' then you pretty much present yourself as insensitive to the issues," said Alexander, who is black.

"The issue of racial tension has been a part of American history since its settlement."

Delrish Moss, who has been police chief of Ferguson, Missouri, since May and is black, said he had negative encounters with police when he was growing up, including being called racial epithets.

"There are communities that have long perceived us as oppressors, there are communities that have long perceived us as the jackbooted arm of government designed to keep people under control, and that's one of the things we have to work hard to get past," Moss said.

"I'm glad it's being addressed ... because the only way to get past it is to first acknowledge the existence of it."

Leaders of the Black Lives Matter movement were less enthusiastic.

DeRay Mckesson, Campaign Zero co-founder, said he looked forward to Cunningham's comments being backed up by deep, structural changes to policing and the criminal justice system.

Lieutenant Bob Kroll, head of the Police Officers Federation of Minneapolis, thought Cunningham's statement went too far. In his city, two white officers fatally shot a black man last November.

"Our profession is under attack right now and what we don't need is chiefs like him perpetuating that we are all bad guys in law enforcement," Kroll said.

"I think it's an asinine statement. ... We've got officers dying on almost a daily basis now because of this environment, and statements like that don't help."

Source: Agencies