Police arrested at least 19 Black Lives Matter protesters on Friday after the group blocked roads near airports in London and Birmingham and staged protests in two other cities.
"This morning we shut down major transport hubs because the conventional avenues to justice have been shut down to us," the Black Lives Matter UK group said on Twitter and Facebook.
"Friends and families of those killed in custody have been failed by police, the judiciary, the IPCC (Independent Police Complaints Commission) and the legislature," the group said. "We stand with them."
The protests were timed to coincide with the fifth anniversary of the death of Mark Duggan, a black man who was shot in his car by police in Tottenham in north-east London.
Duggan's death in 2011 sparked protests that led to rioting in Tottenham and other parts of London and other cities.
London's Metropolitan Police said officers arrested 10 people early on Friday after they blocked an approach road leading from the M4 motorway to Heathrow Airport.
West Midlands Police said five people were arrested for obstructing the A45 road in Solihull, which leads to Birmingham Airport.
Nottinghamshire Police said they arrested three women, aged 30 to 50, and a 30-year-old man "on suspicion of causing the wilful obstruction of a highway" after they blocked a tram line in Nottingham city centre.
Some protesters in London, Birmingham and Nottingham lay down on the road and chained themselves together.
Other protesters displayed banners saying "This is a crisis" and "Delays inevitable, injustice system failure."
"No justice, no peace," read the message on one placard in Birmingham, alongside others saying "Black Lives Matter" and "White silence is violence."