Police and protesters in standoff outside of White House over Floyd's murder

Protesters and police officers were in a standoff outside the White House in the early hours of Saturday as a fourth day of protests sweeping across the U.S. It follows the death on Monday of an unarmed black man called George Floyd.

It's since emerged that the Minneapolis man died after being pinned by the neck by a white police officer's knee in the middle of the street.

Video footage taken by an onlooker's cell phone and widely circulated on the internet showed police officer Derek Chauvin with his knee pressed on Floyd's neck while he gasped for air and repeatedly groaned "Please, I can't breathe".

The officer in question has since been dissmissed from the police department and arrested on third-degree murder and manslaughter charges.

Police dressed in riot gerar were positioned around the White House as crowds gathered.