Hundreds of people are expected to attend day's memorial in Minneapolis for African American George Floyd, who died in police custody last month.
The death of Mr. Floyd, whose neck was pinned under a white officer's knee, has sparked huge protests over racism and police killings of black Americans.
The tribute comes despite fears over coronavirus at large gatherings.
New charges were announced on Wednesday against all four of the now sacked officers present at Mr. Floyd's death.
The charge against Derek Chauvin has been elevated to second-degree murder while the other three officers, previously uncharged, face counts of aiding and abetting murder.
Former President Barack Obama and Meghan, the Duchess of Sussex, are among senior public figures who have offered their support to the protesters.
They were joined on Wednesday by former Defence Secretary James Mattis, who also attacked his former boss President Donald Trump, saying that he stoked division and had abused his authority in his reaction to the protests.
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