LONDON (Reuters) – British anti-racism protesters briefly clashed with mounted police on Saturday after thousands gathered in central London to voice their anger at police brutality after the killing of George Floyd in Minneapolis.

After a largely peaceful day, small numbers of protesters near Prime Minister Boris Johnson’s Downing Street residence threw bottles at police, and mounted officers charged at protesters to push them back.

Earlier more than a thousand protesters marched past the U.S. Embassy on the south bank of the River Thames, blocking traffic and holding placards.

Thousands of protesters had also crowded into the square outside parliament, holding placards saying “Black Lives Matter” and ignoring government advice to avoid large gatherings due to the risk from coronavirus.

“I have come down in support of black people who have been ill-treated for many, many, many, many, years. It is time for a change,” said one protester, 39-year-old primary school teacher Aisha Pemberton.

Another protester, 32-year-old IT specialist Kena David, said Britain was guilty of racist abuses too. “Everything you see around you is built off the backs of black and brown bodies.”

Demonstrations also took place in other British cities, and reclusive street artist Banksy published a new artwork online which showed the U.S. flag being set alight by a candle that formed part of a memorial to an anonymous, black, silhouetted figure.

Saturday’s protests reflect global anger over police treatment of ethnic minorities, sparked by the May 25 killing of Floyd when a white police officer detaining him knelt on his neck for nearly nine minutes as fellow officers stood by.

Tens of thousands of people chanting “no justice, no peace, no racist police” marched through central London on Wednesday. Demonstrators took to the streets in many European and Asian cities on Saturday.

Before Saturday’s protest in London, the U.S. ambassador to Britain, Woody Johnson, issued a statement condemning Floyd’s death and said America needed to do more to fight racism and injustice.

“It is through peaceful protests that injustice is most successfully addressed,” he said.