- 6 updates
The mother of black teenager Michael Brown, who was shot dead by police in Ferguson, said she hopes the protests sparked by his death will make a difference.
Lesley McSpadden said she was overwhelmed by the "sea of people" as thousands turned out to take part in a march on Washington.
She added: "If they don't see this and make a change, I don't know what we're going to do."
Nearly two dozen civil rights protesters have been arrested in Boston in the US.
Police said the demonstrators were detained for disorderly conduct after trying to block a highway.
Thousands are taking part in protests in New York, Washington and California, which have so far remained peaceful.
It comes after three unarmed black men were killed by police in recent weeks.
Hundreds of protesters have gathered near New York's Washington Square Park, to join a march against "police brutality" following the recent deaths of two unarmed black men at the hands of white police officers.
Bearing signs emblazoned with the slogan 'stop police brutality' the crowd marched towards NYC's police headquarters chanting "I can't breathe", the dying words of police choke-hold victim Eric Garner.
The New York march coincides with another 'justice for all' march being held in Washington today.
Thousands of demonstrators streamed through the streets of Washington singing, shouting and chanting against the recent police killings of unarmed black men.
Shouts of 'Black lives matter', 'Hands up, don't shoot', and 'I can't breathe' were heard as a wide range of Americans from different ethnic backgrounds walked peacefully through the capital.
Crowds of protesters have filled the streets leading up to Washington's capitol hill as they march for 'justice for all' following the deaths of two unarmed black men at the hands of white police officers.
Carrying signs which read "Black Lives Matter" and "Who do you protect? Who do you serve?", the crowd gathered in Freedom Plaza today before marching up the capital's Pennsylvania Avenue.
More than 10,000 protesters have gathered in Washington today to take part in a march against "police brutality" following the deaths of two unarmed black men at the hands of white police officers in recent months.
The families of Michael Brown and Eric Garner, both of whom died in incidents involving white police officers, are among the crowds of protesters who are expected to march to the Capitol later today.
Last month's decision by a US grand jury not to indict the officers involved in the deaths of 18-year-old Brown and 43-year-old Garner, who gasped "I can't breathe" while being arrested in New York, has led to outrage across America and numerous protests have already been held.