World leaders have voiced condemnation over the May 25 killing of George Floyd by police in the United States, as his death prompted waves of angry and sometimes violent protests in cities across the U.S. and around the world. 

U.S. President Donald Trump has faced heated criticism for using force outside the White House to dispel peaceful demonstrators against racial injustice.

Federal police on Monday abruptly fired rubber bullets and tear gas into a peaceful crowd in Lafayette Park outside the White House, permitting Trump to walk through for a brief photo-op at a historic church that had suffered damage the night before.

From Amsterdam to Nairobi, protesters highlighted allegations of abuse of black prisoners by their jailers, social and economic inequality, and institutional racism lingering from the colonial pasts of the Netherlands, Britain and France.

UN Secretary-General Antonio Guterres has condemned racism and called for efforts to end inequality and discrimination.

"Racism is an abhorrence that we must all reject… Addressing inequality & discrimination, strengthening support for the most vulnerable and providing opportunities for everyone," he tweeted.

He also urged law enforcement to "show restraint in responding to demonstrations."

While peaceful protesters joined the Black Lives Matter march in Hyde Park in London, UK Prime Minister Boris Johnson condemned the killing of the unarmed African-American man by police.

"I think what happened in the United States was appalling, inexcusable," Johnson told MPs in parliament, in his first public comment on the case. "We all saw it on our screens and I perfectly understand people's right to protest what took place," he added. "Obviously I also believe that protests should take place in a lawful and reasonable way." 

But Johnson avoided answering questions as to whether he had raised the matter with Trump.

Iranian Supreme Leader Ayatollah Ali Khamenei said the police killing shows the "true face" of the United States and its oppression of the peoples of the world, including its own.

"The fact that a policeman has cold-bloodedly pressed his knee on the throat of a black man until he died and that other policemen watched on without doing anything is nothing new," Khamenei said in a televised speech on Wednesday.

"It is the true face of America, it's what it has always done all over the world – in Afghanistan, Iraq, Syria and other countries, and before that in Vietnam… It is the normal course of action of the United States, it's the true face of their regime," Khamenei said.

"These are realities that have always been camouflaged or hidden, but they are not new," he said.

Asked about Trump's threat to use military force against protesters, Canadian Prime Minister Justin Trudeau paused for 21 seconds and took aim at social injustice.

"We all watch in horror and consternation at what is going on in the United States," he said. "It is a time to pull people together ... it is a time to listen. It is a time to learn, when injustices continue despite progress over years and decades."

But he avoided directly criticizing Trump's handling of the situation.

German Foreign Minister Heiko Maas called the anti-racism protests "understandable and more than legitimate."

"I hope that these peaceful protests won't slide further into violence, but even more than that I hope that they will make a difference in the United States," Maas said.

(With input from Reuters, AFP) 

(Cover: People wearing protective face masks hold up signs during a protest against the death of George Floyd who died in police custody in Minneapolis, London, Britain, June 3, 2020. /CCTV)