The growing calls to dismantle or reimagine US police departments have put pressure on Biden and other Democratic leaders, who favour policing reforms but are wary of adopting a loaded phrase that some Democrats fear could be a divisive election issue.

President Donald Trump and other Republicans have seized on the "defund the police" slogan to suggest Democrats are bending to extremists at the expense of public safety.

The term is being used by activists to propose eliminating or cutting spending on police departments, often the largest expense for municipalities, and instead funnelling the money to programs for education, social welfare, housing and other community needs.

Protests have roiled US cities for more than two weeks since the death of George Floyd, an unarmed black man, after a white Minneapolis police officer kneeled on his neck for almost nine minutes.

Biden, the former vice president, met with Floyd's family in Houston for more than an hour on Monday to offer his sympathies.

"I don't support defunding the police," Biden said afterwards in an interview with CBS. "I support conditioning federal aid to police, based on whether or not they meet certain basic standards of decency and honorableness."

Biden had previously called for a $US300 million investment in policing, contingent on officers mirroring the diversity of their communities. In a statement, his campaign said he supports funding for better training, body cameras and community policing.

Trump on Monday said on Twitter that, "Radical Left Democrats want to Defund and Abandon our Police" despite low crime rates. "Sorry, I want LAW & ORDER!"

Biden and Trump will face off in the November 3 election. At a law enforcement roundtable on Monday, Trump also said he was looking at various police reforms but vowed, "There won't be defunding."

Biden's stance echoed that of Democrats in congress, who on Monday unveiled sweeping legislation to combat police violence that stopped short of cutting funding for local law enforcement agencies.

Progressives are pushing for more. Senator Bernie Sanders - who promised to hold Biden accountable after ending a presidential campaign and endorsing the former vice president - has called for slashing all federal funding for police departments accused of violating people's civil rights.

Several people serving on "unity" task forces set up by Biden and Sanders support shifting funding from policing to community services, they told Reuters in interviews.

"Everyone recognises the centuries of systemic oppression and white supremacy and the fundamental failure of the criminal justice system," said Linn County, Iowa, supervisor Stacey Walker, a member of Biden's criminal justice policy task force though not speaking on its behalf.

"If that doesn't open up a new political opportunity for sweeping reform, then I don't know what will."

Varshini Prakash, executive director of the environmental group Sunrise Movement and a member of Biden's task force on climate change, said it was less important for Biden to carry a "cardboard sign saying 'Defund the Police'" and more important for him to "articulate a real transformational vision ... beyond policing and incarceration".

Any cuts to police budgets are likely to be met with stiff opposition from public sector unions, which finance and organise on behalf of Democrats.

Bill Johnson, the head of the National Organisation of Police Associations, a nonprofit trade group, said Biden was right to suggest more funding for both police as well as other services.

"Taking away police isn't going to solve these other problems," Johnson said.

Vanita Gupta, the former civil rights chief at the US Department of Justice and a member of Biden's criminal justice task force, said the protests reflected a growing consensus that flawed policing is just one aspect of a deeper issue.

"Police reform alone is not going to solve the problem of police violence," she said. "It really is going to require fundamentally looking at what kind of investments and priorities have been made in black and brown communities over many years."

Australian Associated Press