Hillary Clinton has said the US criminal justice system is "out of balance" and she supports federal reviews of police-involved deaths of unarmed black men in Ferguson, Missouri, and New York.
Mrs Clinton said the cases of Eric Garner and Michael Brown, which have stirred a national conversation on race and law enforcement, show the need for federal funds to be used for best practices, "rather than weapons of war".
The former first lady is the leading Democratic contender to succeed President Barack Obama should she seek the presidency again.
Mr Obama is the nation’s first black president, and the two cases could shape how Mrs Clinton talks about civil rights and seeks to maintain support among African-American voters, a key Democratic constituency.
Mrs Clinton’s remarks at a women’s conference in Boston were the first time she has spoken about the two cases in the aftermath of findings by grand juries and racially charged protests around the nation.
Civil rights leaders have criticised the grand jury decisions not to charge a white police officer over the chokehold death of Mr Garner in New York and a separate decision not to charge a white officer who shot and killed 18-year-old Mr Brown in Missouri.
‘Full and fair accounting’
Mrs Clinton, a former secretary of state, said the families and communities deserved a “full and fair accounting” and the deaths had forced the nation to “grapple with some hard truths about race and justice in America”.
She noted that black men are more likely to be stopped and searched by police, charged with crimes and sentenced to longer prison terms.
“We have allowed our criminal justice system to get out of balance,” Mrs Clinton said. “And I personally hope that these tragedies give us the opportunity to come together as a nation to find our balance again.”
At the Massachusetts Conference for Women, Mrs Clinton expressed support for reviews by the Justice Department and Mr Obama’s recent announcement of a task force on policing.
On Wednesday evening, thousands of demonstrators disrupted New York City traffic after the grand jury decision in the Garner case became known.
Mostly peaceful protests sprung up at locations throughout Manhattan, including Grand Central Terminal, Times Square and near the Rockefeller Center, after the panel returned no indictment against Officer Daniel Pantaleo in the death of Mr Garner in July.
The US Justice Department said it was investigating to determine whether Mr Garner’s civil rights had been violated.
The 43-year-old father of six was accused of illegally selling cigarettes on a sidewalk when Mr Pantaleo put him in a chokehold from behind and tackled him with the help of other officers. Police said he had resisted arrest. The city’s medical examiner ruled the death a homicide.
Debate fuelled
The deadly encounter on Staten Island, New York City’s least populous borough, was captured on a video that quickly spread over the internet and fuelled debate about how US police use force, particularly against minorities.
US president Barack Obama said the grand jury decision spoke to “the concern on the part of too many minority communities that law enforcement is not working with them and dealing with them in a fair way”.
The decision poses the biggest challenge yet for New York Mayor Bill de Blasio, who came into office in January promising to mend strained relations between black New Yorkers and the police department.
It was the second grand jury in just over a week to decline to prosecute a white policeman in the death of an unarmed black man.
The decision by a panel in the shooting death of black teenager Michael Brown in Ferguson, Missouri, sparked a spasm of violence, with businesses burned and looted in the St Louis suburb.
By contrast, the New York protests were civil, with about 30 arrests by mid-evening. Police were clearly showing restraint and allowing demonstrators to block traffic briefly before coaxing them to move on.
Marchers snaked through the streets for hours, chanting and bumping up against throngs of tourists in New York for the holiday season. Disparate clusters of protesters crossed through Times Square a number of times, and one group brought traffic on the West Side Highway along the Hudson River to a standstill.
Later, after marching from Central Park to lower Manhattan, some protesters crossed a bridge into the borough of Brooklyn.
In one of several “die-ins”, demonstrators lay on the pavement in silent protest about a block from where the Christmas tree lighting ceremony was under way at Rockefeller Center. Police blockaded the street, preventing marchers from interrupting the nationally televised event.
About a thousand people packed into the ornate main hall of Grand Central Terminal for a noisy but peaceful protest.
The Justice Department said it would investigate the Garner case and is already looking into the circumstances of the Missouri shooting.
‘Expeditious investigation’
"Our prosecutors will conduct an independent, thorough, fair and expeditious investigation," US Attorney General Eric Holder told reporters in Washington. "In addition to performing our own investigative work, the department will conduct a complete review of the material gathered during the local investigation."
Legal experts say that while there is no explicit law against chokeholds, their use is prohibited by New York police regulations. Any violation, however, would not necessarily constitute a crime, they said.
Mayor de Blasio praised New York Police Commissioner Bill Bratton’s efforts to bridge a long-standing divide between police and minority groups, but Mr de Blasio also said he had warned his African-American son to take “special care in any encounters with police officers.”
In a statement released by the police union, Mr Pantaleo expressed his condolences to Garner’s family.
“It is never my intention to harm anyone and I feel very bad about the death of Mr Garner,” he said.
But at a news conference, Mr Garner’s widow Esaw Garner rejected Mr Pantaleo’s sympathies.
“There’s nothing that him or his prayers or anything else will make me feel any different. No I, don’t accept his apologies. ...
“He’s still working. He’s still getting a pay cheque. He’s still feeding his kids, she said. “And my husband is six feet under and I’m looking for a way to feed my kids now.”
Press Association/Reuters