US President Donald Trump on Friday said that he has spoken with the family of George Floyd, the African American man who died when a policeman kneeled on his neck during an arrest that sparked riots.

Trump said at the White House, “I spoke to members of the family, terrific people”.

As unrest spread, President Trump earlier tweeted: “These THUGS are dishonouring the memory of George Floyd and I won’t let that happen,” in apparent reference to protesters in Minnesota, adding the state’s governor has the backing of the military. “Any difficulty and we will assume control but, when the looting starts, the shooting starts.”

Thousands joined the protests in Minnesota, after death of 46-year-old George Floyd who was arrested on suspicion of using a counterfeit banknote on Monday. A video taken by a bystander shows an officer kneeling on his neck as he is pinned to the ground. Floyd who was unarmed and handcuffed, pleaded that he could not breathe. He was soon after declared dead at a nearby hospital on Monday.

Four policemen involved in the incident have been suspended, while the FBI is investigating the case.

The protests entered their fourth day on Friday and have spread beyond Minnesota, with protests breaking out in several states across the country, including Denver, Colorado and Phoenix.

“I understand the hurt, I understand the pain. People have really been through a lot. The family of George is entitled to justice and the people of Minnesota are entitled to live in safety”, the President said on Friday.

The case was seen as the latest example of police brutality against African Americans, which gave rise six years ago to the Black Lives Matter movement.

Floyd had been detained on a minor charge of allegedly using a counterfeit $20 bill to make a purchase at a convenience store.

Outbreaks of violence have gripped the city as tensions rose since Floyd’s killing.

On Wednesday, demonstrators clashed with law enforcement, looted stores and set fire to shops and a construction site. They were met with police tear gas and rubber bullets.

The protests were reminiscent of those that followed the 2017 death of Philando Castile, who was sitting in his car after a traffic stop in a nearby suburb when an officer shot him.