Around 1,000 demonstrators gathered outside the US Embassy in London before marching down Oxford Street on Wednesday to condemn the decision not to prosecute a police officer for shooting dead black teenager Michael Brown in Ferguson, Missouri.
After listening to a number of speeches the group marched down nearby Oxford Street, which is Europe's busiest shopping street. Traffic was stopped as protesters made their way towards Piccadilly Circus.
The protesters held placards which read "jail racist cops" and chanted "killer police off our streets". Carol Duggan, aunt of Mark Duggan, and Marcia Rigg of the Sean Rigg Justice And Change campaign both spoke at the event.
Mark Duggan, a young black man, was shot dead by a police officer in London in August 2011 sparking riots across the city, while Sean Rigg died at Brixton police station in 2008. Marcia Rigg is Sean Rigg's sister.
Ms Duggan told the crowd: "We need to send a message to Mike Brown's family. We feel the pain, we know the pain, of losing somebody at the hands of the police. That is why we stand in solidarity with the community of Ferguson. I feel they are very strong and brave people."
She went on: "They've come to a point in Ferguson where there is no turning back. They have to carry on fighting. They have to see this through. We have to stand behind them because you know what happens there will eventually happen here."
Ferguson was engulfed in serious civil unrest following a grand jury's decision on Monday not to charge police officer Darren Wilson for shooting Mr Brown.
Ms Rigg said: "Burning and looting - we don't condone these acts - but I for one and I'm sure people around the world understand the frustration and anger that the people are feeling when our loved ones are murdered on the streets. What else are we supposed to do?" She added: "All we keep getting are lying and corrupt officers murdering our loved ones."
The London protest was organised by campaign group Stand Up To Racism. The event in Grosvenor Square was noisy but non-violent. The crowd appeared to swell to more than 1,000 people as supporters of the London Black Revolutionaries movement joined in.
Many held candles and a minute's silence was observed to remember people killed by the police around the world. Demonstrators spilled out of a designated area for the protest and lined up against the fence of the embassy. Many held banners reading "black lives matter", which have been used widely in the US.